On a similar note. I wonder what was taken out. Obviously we have the gospels that didn't quite make the cutand the Apocrypha. What other omissions were taken out from the fables because they didn't tie up?
The obvious response would be the so-called Secret Gospel of Mark. I'm relatively ambivalent about its authenticity and don't really think it can be proved either way. However, in terms of your question I think it doesn't really matter as it is pretty much what we might expect to be omitted were it original.
However, here I tend to almost agree with the asinine Geisler. There's sufficient embarrassing material within the NT -especially the gospels - to make it a reasonable assumption that redaction in that direction perhaps did not happen so much.
In the first instance, although the formation of the canon was a fourth century occurrence it was basically building on the popular tradition of the churches. It wasn't exactly an X-Factor style vote-off but equally it wasn't far off - the most popular and therefore most accepted texts were the ones which made the cut. And whatever the merits of the 4 canonical gospels, I think it is difficult to argue that any of the non-canonical ones are 'closer' to the original tradition/truth than the 4 - or, rather, the 4 they picked were the best they had.
Given that - e.g. a relatively widespread use and popularity of the canonical 4 gospels - I think that the idea of deliberate omissions is something we would never be able to truly have any idea about. If you assume - as the early Christian church did and some later Christian fools do - that the gospels were written by the people whose names were eventually appended to them then altering by either addition or omission becomes a very difficult act for a christian.
As far as we can see, this might have happened - the obvious example being the end of Mark. But even that appears to be a case of "this doesn't quite end properly, let's end it in an 'orthodox' manner and do it quickly". The brevity of the end I think (and this is my interpretation, rather than any scholarly opinion) suggests a degree of tentativeness to the conclusion, as though the writer was aware that something was missing but wasn't willing to thoroughly pretend to be the author and extend things out for a chapter. I'd suggest that this isn't an example of deliberate alteration in the sense of trying amend something that the author said which wasn't comfortable for later generations, but rather an honest (by C1-3 standards) attempt to fill in what Mark
should have said. The success of it is attested by the fact that it wasn't until the mid C19 that the ending of Mark was seriously questioned. And even then, it was only the discovery of Codex Vaticanus which prompted it.
Long diversion, I'm aware, but the point of it is that what is clearly an interpolation to everyone except idiots and DOC was actually unsuspected and unspotted for centuries. It made it into the canon and was then reproduced endlessly. Without suspicion.
This is why one of the most accepted scholarly explanations is that the original manuscript of Mark was in some way damaged and lost the ending. Because the change was so quick and so widely accepted - we have nothing to suggest that there were competing versions of Mark when the canon was discussed - it may well have been made at first generation of manuscript.
With that in mind, I think it is probably quite unlikely that there were significant omissions to the now canonical gospels between them being written and being accepted as canon. And just to clarify, I focus on canon precisely because once something is canonical significantly differing versions become problematic. But again, I don't think that there is anything in the sources to suggest that there were debates about verses omitted in the accepted gospel in certain areas but there in others. As far as I recall, it was assumed that the gospel of Luke in Caesaria was the same as the gospel of Luke in Antioch.
This is hardly surprising - the canonical gospels were relatively quickly accepted amongst the early christian communuties. There was therefore only a short space of time where they were editable - once everyone was using them, across the community any alterations had the potential to be visible. And again, there was a standing disincentive because the entire point of the texts was that they were accepted as being from apostolic hands - who would have the temerity to change them?
So my supposition (DOC note that word, you might find it useful) would be that there probably was not much omission from the canonical texts after a certain period. What went on before then is entirely lost. We simply have no knowledge of how these texts were transmitted and when.