Something frustrating about early Church history is that astonishingly few writings have survived from the most formative periods.

Okay, we have somewhere between seven and thirteen letters from Paul during the 40s and 50s CE.We don't have any of the correspondence he was responding to.

From c.50 to c.150 we have a thin handful of documents -- one letter from Clement, some writings from Ignatius, some from Polycarp. Papias, who might have learned from the original Apostles, wrote five complete treatises on doctrinal issues, of which literally nothing survives but two or three badly damaged quotes in Eusebius. It's a disaster area until c.150 or even c.200, after which letters started to be preserved more systematically.