A suggestion: Perhaps the name/term 'Pontius Pilate' was used by some writers as a general term for all prefects of Judea under Tiberius. This would make some sense of the ambiguity in Josephus re dating Pilate. As demonstrated by Daniel Schwartz, Pilate was in Judea from 18 c.e. to 36/37 c.e. - approximately 19 or so years, an unusually long period of time. Perhaps this long period of rule was not by a specifically named Pontius Pilate - but the term refereed to all the prefects of Judea under Tiberius. (whether by Rome or Jewish writers...)Peter Kirby wrote:
<snip>
So, to put a hypothesis out there plainly, I would like to suggest that the stereotyped phrase "before Pontius Pilate" in connection with Jesus' suffering and death found in second century writing connected with the Roman church had a certain propaganda value. Without actually naming the target and giving him a place of dignity in their professions of faith, the phrase would have a chilling effect on the listener when understood as a condemnation of him who is not named. The hypothesis cannot really rise above a conjecture, but it has the advantage of being the only explanation to date as to why it is such a frozen phrase. That is, other than the old chestnut that it was used to lend specificity to the historical setting. (Although not perfect, there may be a modern analogy of sorts.)
Such a suggestion would also make sense of the early dating for the crucifixion found in the Acts of Pilate. i.e. by using Pontius Pilate as a sort of generic name for prefects under Tiberius, the Jesus crucifixion story was able to entertain crucifixion scenarios from 7th year of Tiberius to around the 15th year of Tiberius - and even to the end of the rule of Pilate in 36/37 c.e.
Thus, not a case of a very long rule for Pilate (the ambiguity in Josephus) but a case of the term Pontius Pilate being a catch-all term for Roman prefects in Judea under Tiberius. (Perhaps one such prefect happened to be named Pontius - but no actual dating could be detailed re the Josephus ambiguity...)