Somewhere archaeologists will find some reference to the census of Caesar and when it was given. Then we will know exactly when Jesus was born.........
Alas, each census took years and were done regionally, so unless you get the memo that says “Palestine,” no dice.
As an aside, the most likely candidate for the census at issue was something like 10-12 BC — although there is another one 6 BC or so that may be in play.