Good point! I totally forgot about that. But I just finished replaying Remake, and the letter from Ada's boyfriend in which he explains the password thing is actually the only document with her name (in this game at least). And we don't see Chris again after that until RE5 (except for CV, but at that time he wasn't doing the job he's doing today). So no matter how often (if at all) Ada's name comes up in any documents from RE2, 3 or 4, Chris probably hasn't read them.
Also, since we don't know what exactly is canon about RE1 (since Chris and Jill's scenarios don't seem to coexist like Leon and Claire's in RE2), we don't know if Chris ever read John's letter, or if it was Jill. Even if he did, though - it says just "Ada." There's no "Wong" anywhere, and I guess there's more than just one Ada around. (I remember having a woman with that name in my Spanish course last year.)
Someone else made another good point by saying that Chris would naturally remember the names of people who work with Wesker, but for all I know, Ada never worked with him again after betraying him in RE4, and I'm still sure Leon left her out of his famous "Kennedy Report".