You are committing a grave exegetical mistake! You are reading back into history from our time. You are insisting that ancient cultures all had reliable time and calendar systems whch all the people knew and used. In fact, except for the Babylonians, none really had calendars which we can accurately correlate to today's dates! The Jews adopted their calendar, but the majority of the common people did not use or refer exclusively it.
The Romans were constantly revising their calendar as new astolonomical data became available. Basically, keeping the feasts, for the Jews, honouring Caesar and the gods for the Greeks and Romans, were the main motives for keeping calendars. So those changes alone made for confusion in dating events.
To expect total accuracy from a people without watches or calendars, who kept feasts and holidays because the priests and scribes reminded them, let alone accurately dating events by year simply shows ignorance of how all ancient cultures worked.
More than that, I think you are focusing on this trivial side issues, rather than facing up to the real issue of the claims of Jesus Christ on your life. On Judgement Day, do you plan to stand before the throne of God, and say "But I didn't understand why they didn't date Jesus life better!" Because you will hear Jesus say, "Begone, I never knew you!"
Instead, consider that Jesus came to die for your sins on the cross. And he rose again from the dead! Repent and believe, is my take home for you!