Durn, wish I'd called them sooner!
I just spoke with Davidsons. The woman I spoke with said if we wanted to, we *could* start by just sending in work samples and didn't need to get testing done right away. Wish I'd have known that! Ah, well. Live and learn, and people, call!
She also said that we didn't need new letters, didn't need to send in a full application -- just an update with any new information.
Still looking at doing the WISC, though, to satisfy personal curiosity.

I spoke with a tester this morning who works with one of our local public schools and has tested kids for Davidson before; I liked her a lot and think we'll probably go that route.
As for doing the WIAT at the same time, Dottie -- quite honestly, it's not in the budget at this point. I don't think his scores will have gone far in either direction -- or, I should say, I don't think they'll have dropped since his math has taken off in the last few months and he's out of his mind with the reading (in a good way). I could be wrong, but they were pretty high to begin with and, since a big reason for retesting is Davidson's (his school could care less about our private results), I think we'll leave good enough alone there.