Even more reason to think Acts 1:20 is fulfilled by God's "chosen vessel" in Acts 9:28 rather than by lot.
Compare Acts 1:26 " Matthias . . . was numbered with the eleven apostles," and Acts 9:26
" And when Saul was come to Jerusalem, he assayed to join himself to the disciples: but they were all afraid of him, and believed not that he was a disciple. 27 But Barnabas took him, and brought him to the apostles, and declared unto them how he had seen the Lord in the way, and that he had spoken to him, and how he had preached boldly at Damascus in the name of Jesus. 28 And he [(Paul)] was with them coming in and going out at Jerusalem."
We don't know what happened to Matthias, but we know that after that, Paul 'fell over himself' telling people that he was an "APOSTLE". We don't have any evidence that the other Apostles rejected him or censured him for such activity. Peter certainly never did, he even mentioned Paul by name in one of his epistles, and in contrast to contradicting Paul's claim to be an Apostle, says almost 'matter-of-factly' that Paul's letters are "scriptures".