How much resurrection evidence should we expect to be mentioned?

When critics of Jesus' resurrection object to something like the lack of mention of the appearance to more than five hundred (1 Corinthians 15:6) in sources other than Paul or the lack of mention of the guards at the tomb in sources other than Matthew, we should ask what we ought to be expecting from these sources. The critics' assumptions about what we should expect may be wrong, and we ought to be careful to not accept false assumptions.

One factor to keep in mind is that though the early Christians thought highly of Jesus' resurrection and gave it a lot of attention, they were substantially less focused on it in apologetic contexts than many people are today. Things like prophecy fulfillment and the other miracles of Jesus and the apostles were much more prominent in ancient Christian apologetics than they are among modern Christian apologists and skeptics.

There's also the fact that the early Christians were historically closer to the events under consideration. Certain things were taken for granted, widely accepted, and so forth that aren't so today. Similarly, we often assume something like the existence of certain people, particular events, the authorship of certain books, etc. in the modern world with little or no argumentation, since those facts are currently widely accepted, often not disputed by anybody. Some of what critics challenge today in the context of early Christianity was widely corroborated by non-Christian sources in the earliest years of the religion (e.g., the empty tomb, the authorship of the gospels).

Furthermore, Christianity was a movement involving many individuals who were providing arguments and evidence for the religion in one way or another. It's not as though Paul was unaware of the existence and activities of other apostles, the gospel authors were unaware of the existence of other forms of communication about Jesus and other gospels, etc. They were making a group effort, and no one source would have thought that everything depended on him.

Sometimes the early Christians are explicit about leaving out some of the evidence they're aware of, as John 21:25 illustrates. In other contexts, the omissions are implicit. The resurrection appearances to non-Christians who then converted to Christianity, most significantly James and Paul (though there likely were others), aren't mentioned in any of the gospels and are absent from some of the other New Testament documents, and Acts doesn't mention the appearance to James, for example. (For the evidence that the pre-resurrection unbelief of Jesus' brothers is historical, see here.) It would be absurd to argue that these sources who left out such resurrection appearances were unaware of them all or unaware of the evidential significance of them, for reasons like the ones discussed in the post just linked. So, it's a demonstrable fact that the early Christian sources often left out substantial lines of evidence that they were aware of for the resurrection.