Can I revert to a previous version of a waveform file after saving?

No, I don't think so. We get this question from time to time, and I'm not aware of anybody who's ever been able to achieve any sort of success at all with this, I'm afraid. If you did this in Waveform view - which I'm presuming you were using - then each time you make a change to a file it's stored as part of the temp file system. This means that while Audition has that particular file open, and it remains working, that undos up to the level you've specified can be gone back through. The moment the file closes or gets corrupted, then the temp file gets trashed, so no further work on it is possible. This is why we always tell people to work on a copy, not the original. 

One of the reasons that this happens, incidentally, is that Audition by default shares a temp space with the operating system, and unless you take steps to stop it, the OS can resize its temp file at will - within the same directory. I'm sure you can see how this could lead to problems, especially when you realise that with big files, and even a small number of undos, Audition's temp file can get massive. One way to mitigate this (apart from stopping the OS from doing this, which you can do) is to move Audition's primary temp file to a different location, ideally on another physical drive, but at least into a different folder.