Historians of reddit have to deal with this on a recurring basis. It's hard when textual refs stop in Josephus and the accretion of centuries of editorial over ur-texts.

Often times people seek to argue by comparison: "we have less evidence Darius or Julius Caesar existed" type arguments about the primacy of contemporary eye witness accounts, distinct from eg economic and architectural evidence.

Fugitive Christians didn't have time to collate the "I was there" takes and now it's Analects.