Rather than being some Christian fabrication, the report that Jesus appeared to the 500 brethren ultimately echoes the testimony from the purported witnesses themselves.
This full article analyzes these four evidences:
• The v3-7 creed relays witness testimony.
• In reciting 1 Cor 15:6, Paul strove to relay testimony.
• The 1st church: “Jesus visited the 500!”
• No one invented the 500 (not fabricated).
This is relevant because it entails that the 1 Cor 15:6 creed was a relaying of what the 500 were themselves saying.
Since c. AD 30, the Jerusalem church was circulating the message of 1 Corinthians 15:6, that Jesus appeared to “the 500 brethren.”
This is relevant because [the 1st church's testimony on such things matched that of relevant witnesses](). (Note: This is different from the evidence above.)1
“The 500 brethren” in fact are the witnesses who saw Jesus appear to them on the mountain at Galilee, as described in Mt 28:16-20.
This is relevant given the Gospel of Mt relays witness testimony (i.e., given that it relays what the relevant witnesses were themselves saying).
If there actually was an appearance (or an ostensible one) of Jesus to “the 500 brethren,” then it is clear that it both was not mentioned in the other gospels and yet would’ve been.
But no, plausibly...
• Arguments from silence must be careful.
• E.g. It’s not clear Lk would’ve mentioned it.
• E.g. It’s not clear Mt would’ve mentioned it.
• E.g. It’s not clear Jn would’ve mentioned it.
But so what? Plausibly…
• Mt hints at a crowd visit in Galilee (see: It was the Galilean Mt. appearance)
• Lk hints at additional visits, of which the 500 would fit well. 1