It was sometimes claimed that a government record of the census still existed into the second century and beyond:
"Now there is a village in the land of the Jews, thirty-five stadia from Jerusalem, in which Jesus Christ was born, as you can ascertain also from the registers of the taxing made under Cyrenius, your first procurator in Judaea." (Justin Martyr, First Apology, 34)
"And yet how could He [Jesus] have been admitted into the synagogue - one so abruptly appearing, so unknown; one, of whom no one had as yet been apprised of His tribe, His nation, His family, and lastly, His enrolment in the census of Augustus - that most faithful witness of the Lord's nativity, kept in the archives of Rome?" (Tertullian, Against Marcion, 4:7)
"For He [Jesus] was from the native soil of Bethlehem, and from the house of David; as, among the Romans, Mary is described in the census, of whom is born Christ." (unknown author [not Tertullian], Tertullian's An Answer To The Jews, 9)
"Let, then, such as trust to instruments of human skill, who may (approving of applying them as attestators of the holy word) inquire into this census, if it be but found so as we say" (unknown author, Five Books In Reply To Marcion, 5:198-203)
"Finally, though never at Rome, on authority he [John Chrysostom] knows that the census papers of the Holy Family are still there." (Catholic Encyclopedia)
"He [an author falsely writing as Cyril of Jerusalem] asks Julius to assign the true date of the nativity 'from census documents brought by Titus to Rome'; Julius assigns 25 December." (Catholic Encyclopedia)
"If verifiable this text [a homily attributed to Jerome] would suggest that Jerome, like Augustine, believed 25 December to be the historic anniversary of Christ's birth on the basis of the putative census records from the time of Augustus." (Susan Roll, Toward The Origins Of Christmas [The Netherlands: Kok Pharos Publishing House, 1995], p. 104)
Some of these claims are problematic, and we don't have much information by which to judge the more credible claims. Justin Martyr's claim is the earliest and the most credible. But Richard Carrier writes:
"Justin Martyr's Apology 1.34 and 1.46 also shows that this is exactly how Christians understood their own history: Quirinius was the first governor of Judaea, and Jesus was born during the census he took there, which happened 150 years earlier. It is believed that Justin wrote his first apology around 155 A.D., which produces a birth year of 6 A.D. (the 150th year before Justin wrote). Justin also claims that one can check the census records to confirm this, but this is certainly a bluff: it is extremely unlikely that Justin checked them himself. He does not say he did, and the information he gives is too vague to suggest he was drawing on an official record. Had he read the actual record, he should have been able to report at least one of the items the record would include: for Joseph there would be a full name, age, name of father or family, residence, occupation, and amount of property, as well as the character and extent of any land and the number of slaves owned. If a baby Jesus would be listed at all in the census records, it would only be as part of this entry. It is also unlikely that just anyone could access such important records--to prevent fraud, they must have been kept under very tight guard and accessible only to Roman magistrates. Cf. Oxford Classical Dictionary, 3rd ed. (1996), s.v. 'census.'"
There are a lot of problems with what Carrier is asserting here.
I have the 2003 edition of the dictionary he cites. It says more than Carrier does on some issues and less on others. The last sentence in Carrier's comments above, prior to his reference to the dictionary, expresses Carrier's opinion. The dictionary doesn't assert Carrier's conclusions. Apparently, Carrier was citing the dictionary only to corroborate some of his more general claims.
Notice that Carrier refers to what Justin Martyr and "Christians" believed. Notice, also, that Carrier suggests that a specific year for Christ's birth, 6 A.D., was still known to these Christians as late as the middle of the second century. Think about the implications of Carrier's argument. He's suggesting that these Christians were interested and knowledgeable enough about the relevant chronological data to keep track of the year of Christ's birth more than a century after the event. He's also suggesting that the alleged contradictions between Matthew and Luke, as well as between earlier and later interpretations of Luke, were prominent and persisted as late as the middle of the second century. If Carrier's suggestions are true, we would expect to see them reflected in other sources. But we don't.
Jack Finegan, in his Handbook Of Biblical Chronology (Peabody, Massachusetts: Hendrickson Publishers, 1999), discusses fourteen different sources who date Christ's birth in the second through sixth centuries (pp. 288-291). Of those fourteen, none give 6 A.D. as the year. The large majority give a year in the closing decade of the B.C. era.
The closest any source gets to the date Carrier assigns to Luke's gospel, Justin Martyr, and "Christians" of Justin's time is 9 A.D. And that 9 A.D. date comes from Epiphanius' description of what was believed by a heretical group of the late second century. But Epiphanius' description of the same heretical group suggests elsewhere that they dated Jesus' birth to "around" 4 B.C. (p. 290) Apparently, either this heretical group, the Alogi, were inconsistent in their own dating or were misrepresented by Epiphanius. But even if they, or some of them, did intend to date Jesus' birth to 9 A.D., that date would be a few years off from what Carrier attributes to Luke, Justin, and other Christians. And that's the closest anybody gets to Carrier's date.
Finegan mentions seven sources who either were contemporaries of Justin Martyr or lived shortly after his time (Alogi, Irenaeus, Clement of Alexandria, Tertullian, Julius Africanus, Hippolytus of Rome, and Origen). All of them give a year in the closing decade of the B.C. era. And Finegan doesn't mention all of the sources he could have. Clement of Alexandria, for example, makes reference to other people who dated Jesus' birth to the same year he did (The Stromata, 1:21).
And Carrier's interpretation of Justin himself is dubious. He refers to how Justin's First Apology was written "around 155 A.D." Eric Osborn dates the work to "shortly after 150" (Justin Martyr [Tubingen, Germany: Mohr Siebeck, 1973], p. 8). Leslie Barnard dates it "between 151 and 155 C.E." (St. Justin Martyr: The First And Second Apologies [Mahwah, New Jersey: Paulist Press, 1997], p. 11). John McGuckin places it "c. 155" (The Westminster Handbook To Patristic Theology [Louisville, Kentucky: Westminster John Knox Press, 2004], p. 200). A recent book on Justin edited by Sara Parvis and Paul Foster, Justin Martyr And His Worlds (Minneapolis, Minnesota: Fortress Press, 2007), places the First Apology at "154-155" (p. xiii). All of these dates are approximations, yet Carrier has to assume that 155 is correct in order to get to his result of "a birth year of 6 A.D. (the 150th year before Justin wrote)".
Leslie Barnard comments that Justin's reference to 150 years is "no doubt a round figure" (St. Justin Martyr: The First And Second Apologies [Mahwah, New Jersey: Paulist Press, 1997], p. 11). In addition to the fact that 150 is the sort of number that somebody would cite if he were rounding off, we see Justin using round numbers repeatedly elsewhere in the same document. In chapter 31, speaking of Jesus' fulfillment of prophecy, Justin writes:
"And He was predicted before He appeared, first 5000 years before, and again 3000, then 2000, then 1000, and yet again 800; for in the succession of generations prophets after prophets arose."
Those are all rounded numbers. Similarly, in chapter 42 of the same document, shortly before the passage Carrier cites:
"The words cited above, David uttered 1500 years before Christ became a man and was crucified"
Again, he's using a rounded figure. Elsewhere, Justin repeatedly cites Matthew's gospel approvingly, treats the accounts of Matthew and Luke as harmonious (Dialogue With Trypho, 78), and refers to Jesus' birth under Herod the Great, distinguishing him from Herod Archelaus (Dialogue With Trypho, 103).
We don't know what year Justin's First Apology was written. The figure Justin cites in the passage under discussion (150 years) is the sort of figure somebody would use if rounding. Justin repeatedly uses rounded year numbers elsewhere in the same document. He accepts Matthew's gospel as harmonious with Luke's, states that Jesus was born under Herod the Great, and specifically distinguishes between that Herod and Herod Archelaus. Several other sources contemporary with Justin or born shortly after his time give a year for Jesus' birth, and all of them, with one possible exception (the 9 A.D. dating discussed earlier), place Jesus' birth in the closing decade of the B.C. era. Those sources include men who had lived where Justin lived, possessed Justin's writings, and thought highly of him.
And Justin is the only source Carrier cites to argue that "Christians" understood Luke's gospel the way Carrier represents it. It's much more likely that Justin was using a rounded figure. Since I reject Carrier's interpretation of Justin Martyr, I don't know of any source in the earliest centuries who agreed with Carrier's interpretation of Luke.
What about Carrier's assessment of whether there was a census record as Justin describes it? It's reasonable to think that Justin might have been speculating or repeating something he had heard without confirming it. But I think that Carrier is overly confident in his conclusion that Justin was "bluffing".
Carrier tells us that, if Justin had seen a census record, he could have mentioned "at least one of the items the record would include". But Justin does mention one of the pieces of information supposedly in the census record: the Bethlehem birthplace. Apparently, Justin thought that the record referred to Bethlehem in some context (because Joseph owned property there or for some other reason).
Besides, why would Justin think he needed to mention the sort of details Carrier asks for? If Justin's claim wasn't being disputed, and he thought that people could access the census record themselves, why would he go into the sort of detail Carrier wants?
And while Carrier thinks that only government officials would get access to the census records, Justin's claim doesn't require that he or anybody else outside of the government had gotten access to such a record without government assistance. A Christian or non-Christian who had been in a position to access such a record could have seen it.
Again, though, I think it's reasonable to question Justin's claim. What's more significant than Justin's claim about such a census record is what's implied by his willingness to make that claim. The claim of a government census record involves a historical interpretation of Luke's account, so Justin's comment tells us how he viewed the genre of the census account in Luke's gospel. And even if Justin was mistaken about the existence of such a census record, he was so confident about the historicity of the census as to expect corroboration of it from the Roman government. Even if his confidence was too high, it's unlikely that he would become so confident if he was living in an atmosphere in which the census account in Luke was being widely questioned or denied. Similar implications follow from the other ancient sources, mentioned earlier, who refer to a census record kept by the Roman government.