While it is certainly not conclusive, there are some commentators who conflate this gathering of the disciples in John 20 with the gathering described in Luke 24. This is mostly due to Jesus' offering them to touch and see his wounds in both accounts as well as the relatively close match chronologically:
Jesus assured them He was actually Jesus of Nazareth and that He was really raised from the dead. Jesus did this for more than the 10 disciples present; Luke mentioned this gathering as including not only the disciples but also those who were with them gathered together (Luke 24:33) and that Jesus invited them to actually touch His body to see that it was real (Luke 24:39-40). - Enduring Word
The text of Luke does say that there were others gathered with the eleven apostles at this particular appearance:
And they rose up the same hour, and returned to Jerusalem, and found the eleven gathered together, and them that were with them, Saying, The Lord is risen indeed, and hath appeared to Simon. And they told what things were done in the way, and how he was known of them in breaking of bread. And as they thus spake, Jesus himself stood in the midst of them, and saith unto them, Peace be unto you. But they were terrified and affrighted, and supposed that they had seen a spirit. And he said unto them, Why are ye troubled? and why do thoughts arise in your hearts? Behold my hands and my feet, that it is I myself: handle me, and see; for a spirit hath not flesh and bones, as ye see me have. And when he had thus spoken, he shewed them his hands and his feet. - Luke 24:33-40
However, it must be noted that Luke records "the eleven gathered together" and so, if this is to be conflated with John, it must be the second time when Thomas was present. This raises yet another difficulty because the second appearance in John (with Thomas present making 11) takes place 8 days after the resurrection:
And after eight days again his disciples were within, and Thomas with
them: then came Jesus, the doors being shut, and stood in the midst,
and said, Peace be unto you. - John 20:26
While Luke has the Emmaus road disciples returning to Jerusalem and finding the eleven gathered with some others on the very same day (assumed) as the resurrection:
And they rose up the same hour, and returned to Jerusalem, and found the eleven gathered together, and them that were with them - Luke 24:33
- The assumption noted above is derived from Emmaus being approximately 12 kilometers (threescore furlongs) from Jerusalem and that those two disciples left Emmaus for Jerusalem the very hour that Jesus left them. It would take approximately 2.5 hours to walk back to Jerusalem.
Indeed, this very uncertainty is manifest earlier in the same Enduring Word commentary when a chronological list of resurrection day appearances is given and the last on the list is an appearance "to the ten disciples":
To Mary Magdalene (John 20:11-18).
· To the other women (Matthew 28:9-10).
· To the two on the road to Emmaus (Mark 16:12-13, Luke 24:13-32).
· To Peter (Luke 24:33-35, 1 Corinthians 15:5).
· To ten of the disciples, Thomas being absent (John 20:19-23).
How this list can be offered and then John 20 conflated with Luke 24 is mystifying but some support is lent for the conjecture that, in the days following the crucifixion of our Lord, the disciples were often met together and that frequently in the company of others.
It should also be noted that the term "disciples" may include some number of the Apostles but is not limited to them unless specifically delineated as such. In the case of the 12 apostles, all of them are disciples, but it doesn’t follow that all disciples are apostles!
The conclusion must be that, while it is possible and perhaps even likely that more than just the 10 apostles were gathered in John 20:19-23, since they often gathered together as part of a larger company, a careful exegetic should not declare it to be other than conjecture.