I apologise if I didn't express this course of events accurately, but I stand behind my earlier post. Perhaps it's better to phrase this as, don't say no to anything until all the cards are on the table. As I said, this advice came from the department head - the person who made me an offer. By saying yes to all offers, the point is to negotiate the best possible outcome. When the schools know that a candidate has multiple offers, they will compete for that student and often top up the initial offer. And of course, no one knows about SSHRC until some time after initial offers go out, so schools expect this kind of shuffling around until the SSHRC results are released. I'm sorry if I represented myself as heartlessly misleading a bunch of schools, while other students were waiting to get in; that's not my style. I'm not at all suggesting that you wait until August 31 to decline. But I think it's fair to say that candidates and schools are both dancing around the offer(s) for a good amount of time.
I sure hope your "accept" is informal and includes the caveat "...but I'm depending on funding." Or even better, ask to defer the decision until after you hear from SSHRC. It's really poor form to officially accept at multiple places and then withdraw.