The earliest gospel is Mark and was written around the 2nd Temple destruction. ~30ish years post-Jesus. Even that gospel is not a primary source (Mark was not hanging with JC) and you need to employ faith to take the events as laid out in the text as factual. 2/2
Imagine if I wrote now arguing Bush was president in 1995, & no other recording can be found, will I get away with it? No cuz there would be a lot of ppl still living that would refute it. U think just cuz it's old times ppl could get away with claiming resurrection? Even Thomas didn't blv that.