Mat asked for the holes in his memory to be filled. The Finns said "Done". Then he asked to be free of Aes Sedai. They said "Done". Then he asked for a way out.

The wishes were granted prior to the price being paid. The second wish happened to be granted by means of an amulet that he had when he got back.

Furthermore, everyone gets wishes. We don't know what happened after Moiraine and Lanfear fell through the door. They might have ended up in different places in Finnland, for all we know. Your speculation regarding Lanfear not getting wishes - because she is Forsaken or otherwise - is just that, idle speculation.

I'm also not sure what you mean by "transmitigation" - people are doing things to each other to lessen the force of something?

I'm also unsure where you come up with the restriction that the wishes can only be about one's own life.

While I favor the Lanfear theory, my point wasn't that I had proven that she was the killer, just that your ridiculous statement that she "could not" be the killer was completely unsubstantiated. The fact that you still had Fain on the list shows that you didn't even know he had been expressly ruled out, and the fact Slayer was on the list ignores the "attack of opportunity" statements made by Jordan. Those are about the only clues we've been given.