Charge TM question

Let's say there are charge moves A, B, and C.

You have A, and use a charge TM and you get B. If you use another charge TM, do you definitely get C or is it possible to get A again?

I could see it being random the second time, but I could also picture a charge TM 'erasing' the current move from the mon's abilities, never to be learned again - so it wouldn't be possible to use 3 charge TMs on the same mon (at least until new moves are released).

Anyone have conclusive evidence either way?