It is possible to "be in two places at once" from Marriott's perspective. You could be checked in for a long-term stay in one hotel and have a short-term stay at another. That doesn't seem to bother anybody. Or you could actually have stayed in two hotels for the same day, if you left one place very late and paid for that night and checked in somewhere else to sleep. The same thing can happen if you arrived very early (say, after a red-eye flight) and checked in, paying for the previous night. Totally legitimate double credit.

Bruce