Maze Runner: The Death Cure (2018)

Continuity mistake: When Newt is straddling Thomas with a knife pointed down at his upper left chest, it's very obvious that the knife goes into his chest, through Thomas' shirt. A few minutes later, when Thomas is kneeling over Newt, after Newt stabs himself in the chest, the stab hole in Thomas' shirt is no longer there and he isn't bleeding. (01:50:45)

Jorgie Girl Davis

Thomas: Look, even if we find Minho, there's no guarantee we'll make it back from this.
Newt: Then you'll need all the help you can then, won't you? Look, we started this together, may as well end it that way, too.

Question: Thomas knew about being tagged. Why didn't he (and the others) have it removed earlier? It didn't appear to be that delicate or complicated a procedure to have it removed. Am I missing something?