I agree with RayMarler's "criteria". Note, though, that "full" means to whatever depth they've drawn the comb. If the comb is really shallow they'll occasionally cap it at that depth when the flow stops, and that's awkward because it's hard to uncap with a knife and not really worth the time anyway, and on the other hand doesn't provide much winter feed for the space it takes up. (I guess that's one small argument in favor of overwintering in double deeps -- there's room to spare for this kind of sloppiness.)
This year I pulled lots of boxes with half capped or even fully uncapped frames and dehumidified them. I already had a dehumidifier on the cellar level to prevent mold, so I just put that in a small unused bathroom next to the stack of honey supers. Finally I put a box fan on the top of the stack. Every open cell I tested was 16% in about two days, although I didn't test before dehumidifying so I don't know how much moisture was removed. The finished product was 16% as well.
I got the idea from a larger scale beekeeper on these forums (sorry, I forget who) who does the same on a much larger scale. I think this will be my technique from now on -- it's so easy to just pull the whole box on your own schedule, especially if you're trying to extract seasonal honey separately. And it's nice to get down to 16%, instead of the borderline ~18% I've gotten in years past, even from fully capped frames.