Contradiction with Matthew 9:9
Acts 1:21 emphasizes choosing a witness from among those who accompanied Jesus from John's baptism, while Matthew 9:9 shows that Jesus called individuals like Matthew later in His ministry.
Matthew 9:9: And as Jesus passed forth from thence, he saw a man, named Matthew, sitting at the receipt of custom: and he saith unto him, Follow me. And he arose, and followed him.
Contradiction with John 6:66-67
Acts 1:21 requires continuity from John's baptism, but John 6:66-67 shows even many disciples left Jesus at one point.
John 6:66-67: From that [time] many of his disciples went back, and walked no more with him.
Contradiction with 1 Corinthians 15:8
Acts 1:21 requires being with Jesus from the baptism of John, while Paul in 1 Corinthians 15:8 claims apostleship despite not witnessing Jesus’ ministry firsthand from that time.
1 Corinthians 15:8: And last of all he was seen of me also, as of one born out of due time. [one...: or, an abortive]
Contradiction with John 1:35-37
Acts 1:21 sets a specific timeline for witnessing, while John 1:35-37 describes different individuals independently following Jesus without being formally chosen.
John 1:35-37: Again the next day after John stood, and two of his disciples;
Contradiction with Luke 23:49
Acts 1:21 expects consistent following, but Luke 23:49 describes how many acquaintances and women followers of Jesus viewed events from a distance, possibly implying sporadic following.
Luke 23:49: And all his acquaintance, and the women that followed him from Galilee, stood afar off, beholding these things.