For me, if you look at posts by Opus and Tracy, you'll find matching tendencies. That doesn't necessarily mean they're the same person. It very well could be because they have known one another a while, hang out a lot online together, reading each other's messages, and have just gradually gotten more and more alike in their writing style.
That's just me speculating, though. I really have no idea what makes anyone else think that. I can only only assume they're seeing what I see.
I'd just already thought that Opus and Tracy were probably the same person so when an admin in this site mentioned it, I figured my assumptions were correct, just because they're privy to more data than we are. As for "Neo", I really haven't seen/heard/read much out of him so I haven't a clue about that one.