Who got what from whom?

NT scholars typically assume that if Matthew and Luke are quoting and editing Mark, they are not just literarily dependent on Mark, but substantially dependent on Mark. He's their source of information. Now, let us compare these three statements:

Reynolds (pp. cxxiii-cxxv) lists about 150 words that are placed on Jesus' lips in John but are never used elsewhere by the Evangelist. Not a few of these are sufficiently general that they would have been as appropriate in the Evangelists's narrative as in Jesus' discourse. D. A. Carson, The Gospel According to John (IVP 1991), 45.

It is interesting to note as one proceeds through the Gospel how often stylistic peculiarities of John appear on Jesus' lips first and only afterwards in John's narrative material (e.g. 2:4; 3:15; 5:17-23; 6:39; 7:33), suggesting that John's own style may at times have been influenced by Jesus' manner of speaking. And it is not quite true that the discourses of Jesus in John are wholly indistinguishable from John's narrate style elsewhere. No less than 145 words spoken by Jesus in John appear nowhere in the Evangelists's narrative material, and many of these are general enough in meaning that we might have expected them elsewhere (Reynolds 1906: cxxiii-cxxv). C. Blomberg, The Historical Reliability of John's Gospel (IVP 2001), 52. 

It is not true that the discourses of Jesus in John are wholly indistinguishable from John's narrative style elsewhere. H. R. Reynolds's much-neglected commentary lists over 145 words spoken by Jesus in John that are never used by the Evangelist elsewhere, and many of these are general enough that they would have been appropriate in narrative as well as discourse. C. Blomberg, The Historical Reliability of the Gospels (IVP, 2nd ed., 2007), 232.

1. I think there's clearly some literary dependence at work. And given the sequence of publication, I take it that Blomberg's statement in his earlier work is indebted to Carson. 

2. However, I think it's highly likely that Blomberg has direct knowledge of the commentary by Reynolds. So he and Carson share a common source. Blomberg is both dependent on Carson and independent of Carson. In other words, I assume he read both. 

In the earlier work, the wording of his statement seems to be influenced by the wording of Carson's statement. There's stylistic carryover. Stylistically, the data in Reynolds is filtered through Carson. 

In theory, it could be that he had the text of Carson right in front of him when he was writing his own commentary, and he consciously paraphrased Carson. But it could also be, and more likely be the case, that Carson's phrasing stuck in his mind, which subconsciously conditioned how he wrote that paragraph. 

And even if he's stylistically dependent on Carson's wording, he presumably had independent knowledge of what Reynolds wrote. It's an interesting question which he read first. Did he read Carson first, which alerted him to Reynolds, then he consulted Reynolds? As a careful scholar, he might double-check Carson's summary interpretation against the original source. 

3. Then there's the relationship of his later work to his earlier work as well as Carson and Reynolds. Did he still have Carson in the back of his mind when he wrote the later book? Seems more likely that in his later work, he paraphrased and abbreviated his own statement in the earlier work–without going back to reread Carson or Reynolds. He may have done that from memory or perhaps had the text of his own earlier work in front of him. 

Yet the statement in his later work shares some wording with Carson that's absent from his earlier work. It maybe that Carson's phraseology was still floating around in Blomberg's mind. 

Finally, we have:

Although John writes in a fairly uniform style throughout his Gospel–even when Jesus is speaking-there are at least 145 words used only by Jesus that appear nowhere in John's narrative sections. C. Blomberg, Jesus and the Gospels (B&H 2009), 181. 

By this stage, Craig may well have a stereotypical memory of original claim that's psychologically detached from Carson. Craig has written this often enough that it's like stock imagery. 

4. This illustrates some of the imponderables of source criticism and redaction criticism, as well as how some reconstructions erect a false dichotomy between firsthand and secondhand knowledge. Sometimes it's demonstrably both.