I have a Google Analytics account (just ONE, as far as I know) and I've seen the UA number change twice in the past two months. Every time it changes, of course, the stats stop recording, since the code on the site no longer matches what's in the account.
I understood that this number doesn't change, as it is unique to my account. This doesn't seem to be the case. Someone on another forum suggested that I've logged into the wrong GA account. That makes no sense to me either.