How Can Paul Say that Jesus Appeared to “The Twelve”?

Here is an interesting question from my Readers’ Mailbag connected to the tradition that Judas Iscariot killed himself soon after Jesus’ death, leaving only eleven disciples.  Did Paul know about this tradition?  Why does he seem to think there were still twelve disciples after the resurrection?

 

QUESTION:

What do you think about Paul saying that Jesus appeared to the “twelve” (Apostles) after his resurrection? (1 Cor. 15:5) I find this to be a big mistake; given the multiple gospel stories...