ABC:1 Corinthians 15

Verse 5
Jim Meritt of Infidels.org states a contradiction exists here and queries "How many apostles were in office between the resurrection and ascension?"

1 Corinthians 15:5 And that he was seen of Cephas, then of the twelve: 6 After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep. 7 After that, he was seen of James; then of all the apostles. 8 And last of all he was seen of me also, as of one born out of due time.

Matthew 27:3 Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, 4 Saying, I have sinned in that I have betrayed the innocent blood. And they said, What is that to us? see thou to that. 5 And he cast down the pieces of silver in the temple, and departed, and went and hanged himself.

Acts 1:26 And they gave forth their lots; and the lot fell upon Matthias; and he was numbered with the eleven apostles.

Matthew 28:16 Then the eleven disciples went away into Galilee, into a mountain where Jesus had appointed them.

Meritt is trying to say Paul should have said there were eleven instead of twelve at the time. However, Paul was writing after the fact when there were once again twelve apostles (now including Mathias, who had replaced Judas). Therefore Paul was justified in using the phrase "the twelve" after the fact, since Mathias doubtless saw the risen Lord as well, even if Mathias was not considered one of the twelve yet.

The term "the twelve" was likely a common way of referring to the twelve apostles at the time Paul wrote that, just as the Beatles frequently were referred to as the "Fab Four" when they were alive. Yes, Paul was referring to a time Mathias wasn't yet considered one of "the twelve" but at the time Paul was writing Mathias had become one of "the twelve."

Even if one really wanted to nitpick like this, Judas didn't technically stop getting considered one of "the twelve" until Acts 1:26, so even if he died a few days before Peter saw Jesus (compare Matthew 27:3-5 and 28:7) he was still considered one of "the twelve." Meritt assumes Judas just stopped being considered one of "the twelve" upon dying which the Bible never states.