I don't think that Mickey know what happened either.
You know, if he would have met face-to-face with Terra (they don't even speak to each other in BBS), I'm sure that while discussing with Ansem the wise (flashback from KH II), he would have recognized Terra (despite being possessed by MX) as Xehanort.
Now that I think, it's odd enough that the name Xehanort didn't ringed a bell for Mickey when he met Xehanort. He knew MX's name for sure, right?
You know, if he would have met face-to-face with Terra (they don't even speak to each other in BBS), I'm sure that while discussing with Ansem the wise (flashback from KH II), he would have recognized Terra (despite being possessed by MX) as Xehanort.
Now that I think, it's odd enough that the name Xehanort didn't ringed a bell for Mickey when he met Xehanort. He knew MX's name for sure, right?