we always buy our annual passes only when we get to orlando.
If by chance the trip is canceled for some reason, that would be money i couldn't get back.
So we buy them when we arrive, when i know 100% that we're actually going to WDW. I still can make resort reservations using the discount rate. You don't need to have the APs when you're making the reservation, only when you check in. And even then, you don't have to. I always tell them that we're off to DTD to buy our passes and they say just show our passes to them once we have them. Which is what we do.