The funny thing about Acts 1 is how there are about 120 "disciples" of Jesus after the "ascension", but only 2 are candidates to replace Judas because only they were witnesses to the baptism of John and to the resurrection

And in those days Peter stood up in the midst of the disciples, and said, (the number of names together were about an hundred and twenty,)

-- Acts 1:15

Wherefore of these men which have companied with us all the time that the Lord Jesus went in and out among us, Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection. And they appointed two, Joseph called Barsabas, who was surnamed Justus, and Matthias.

-- Acts 1:21ff.

Yet Paul claims Jesus was seen resurrected by more than 500 "brethren":

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. After that, he was seen of James; then of all the apostles.

-- I Corinthians 15:6f.

By the time of Acts 1, the twelve disciples of Jesus have become the (almost) twelve apostles, and the not quite disciple followers of Jesus have now been promoted as it were to full disciples.

But Acts poses far fewer "disciples", now more broadly conceived, than Paul's even more broadly conceived "brethren", who were witnesses to the resurrection.

The key to apostleship according to Acts is NOT simply the terminus ad quem of Paul (And last of all he was seen of me also, as of one born out of due time -- I Corinthians 15:8), but the terminus a quo involving the ministry of the Baptist AND the terminus ad quem of the resurrection.

This is why Paul's apostleship was considered illegitimate during his lifetime. He was part of the more expansive group associated with the 500, not with the more restrictive group associated with the 120.

The deal breaker was the missing link to John the Baptist.

Him he knew not.

Paul's insistence on the "apostleship" as a gift of the Spirit (I Corinthians 12:28) is an expansive interpretation based on his own ecstatic conversion experience, which in the final analysis is the basis for his gospel and his claim to be an apostle. Everything about it hangs on his claim to have experienced "seeing" the Lord, simply the "back end" of the deal. It has absolutely nothing to do with seeing the historical Jesus from the time of Jesus' baptism at the hands of the Baptist right on through all the events to the end and witnessing his actual resurrection. Which, in fact, he utterly eschews.

Am I not an apostle? am I not free? have I not seen Jesus Christ our Lord? are not ye my work in the Lord?

-- I Corinthians 9:1

Paul an apostle--not from men nor through man, but through Jesus Christ and God the Father, who raised him from the dead. But I certify you, brethren, that the gospel which was preached of me is not after man. For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.

-- Galatians 1:1, 11f.

Christianity as we know it today is based entirely on this, and it is sinking sand.

You shall be my witnesses, or tell no one about me?

[R]epentance and forgiveness of sins should be preached in his name to all nations, beginning from Jerusalem. -- Luke 24:47

But you shall receive power when the Holy Spirit has come upon you; and you shall be my witnesses in Jerusalem and in all Judea and Sama'ria and to the end of the earth. -- Acts 1:8

And Jesus saith unto him, See thou tell no man; but go thy way, shew thyself to the priest, and offer the gift that Moses commanded, for a testimony unto them. -- Matthew 8:4

Then he strictly charged the disciples to tell no one that he was the Christ. -- Matthew 16:20

And he charged them to tell no one; but the more he charged them, the more zealously they proclaimed it. -- Mark 7:36

And he charged them to tell no one about him. -- Mark 8:30

And he charged him to tell no one; but "go and show yourself to the priest, and make an offering for your cleansing, as Moses commanded, for a proof to the people." -- Luke 5:14

And her parents were amazed; but he charged them to tell no one what had happened. -- Luke 8:56

And he straitly charged them, and commanded them to tell no man that thing; -- Luke 9:21