A quick comment regarding how subsequent Gospel writers often felt an irresistible need to clarify or expand upon their sources.
In the Last Supper story, the Gospel that came to be named after Mark 14 has Jesus declare that one of the twelve who eats with him from the same bowl will betray him.
17 And evening having come, he cometh with the twelve,
18 and as they are reclining, and eating, Jesus said, `Verily I say to you -- one of you, who is eating with me -- shall deliver me up.'
19 And they began to be sorrowful, and to say to him, one by one, `Is it I?' and another, `Is it I?'
20 And he answering said to them, `One of the twelve who is dipping with me in the dish;
IOW Jesus is made to say that one of the 12 who are sharing the meal will betray him. He is not identified here but of course the reader knows who because of vs 10.:
And Judas the Iscariot, one of the twelve, went away unto the chief priests that he might deliver him up to them,....
The writer (or redactor) of Matt 26 perhaps concerned it made Jesus appear unaware of who the traitor was adds material wherein Jesus makes an explicit identification to Judas.
20 And evening having come, he was reclining (at meat) with the twelve,
21 and while they are eating, he said, `Verily I say to you, that one of you shall deliver me up.'
22 And being grieved exceedingly, they began to say to him, each of them, `Is it I, Sir?'
23 And he answering said, `He who did dip with me the hand in the dish, he will deliver me up;...
25 And Judas -- he who delivered him up -- answering said, `Is it I, Rabbi?' He saith to him, `Thou hast said.'
Notice the subtle change in wording regarding the bowl. "One of the twelve who is dipping with me in the dish;" was turned into "`He who did dip with me the hand in the dish, he will deliver me up". The writer of Matt goes further and singles out Judas with a feigned query and Jesus direct identification. This might have been satisfying for this writer, but it creates a new question. How is it possible that no one showed any concern that Judas had just been identified as a traitor?
The writer of Luke 22, reorders Mark and Matt quite a bit as we know, but on the point of the betrayal, he follows Mark in leaving unsaid who was the traitor. Is this because his copy of Matt does not have these additions, or is it because he feels the addition complicated the narrative?:
21 `But, lo, the hand of him delivering me up [is] with me on the table,...23 And they began to reason among themselves, who then of them it may be, who is about to do this thing.
The Gospel John takes the version in Matt and expands further but also tries to explain things at the same time. He makes explicit that Jesus already knew who the betrayer was in his unique foot washing scene:
11 for he knew him who is delivering him up; because of this he said, `Ye are not all clean.'
The readers are fully aware of the traitor even earlier because he follows the Synoptics in telling the readers a few verses before that Judas was the guy.
2 And supper being come, the devil already having put [it] into the heart of Judas of Simon, Iscariot, that he may deliver him up,
Then at the dinner itself this writer attempts to find a way for Jesus to have disclosed the traitor but not to everyone just the ostensible author (John).:
21 These things having said, Jesus was troubled in the spirit, and did testify, and said, `Verily, verily, I say to you, that one of you will deliver me up;'
22 the disciples were looking, therefore, one at another, doubting concerning whom he speaketh.
23 And there was one of his disciples reclining (at meat) in the bosom of Jesus, whom Jesus was loving;
24 Simon Peter, then, doth beckon to this one, to inquire who he may be concerning whom he speaketh,
25 and that one having leant back on the breast of Jesus, respondeth to him, `Sir, who is it?'
26 Jesus answereth, `That one it is to whom I, having dipped the morsel, shall give it;' and having dipped the morsel, he giveth [it] to Judas of Simon, Iscariot.
27 And after the morsel, then the Adversary (Satan) entered into that one, Jesus, therefore, saith to him, `What thou dost -- do quickly;'
28 and none of those reclining at meat knew for what intent he said this to him,
Readers have been trying to make sense of this scene ever since. John asks Jesus which one and he straight-out says it is the one to whom he gives a morsel. He gives it to Judas but somehow John doesn't get it.
There are scores of interesting differences between these versions, even within the individual texts themselves. Just wanted to demonstrate a simple example of the Gospel revisions regarding the dipping into the bowl detail.