I relooked at Publication 4303 -- dedicated to auto and boat donations. I didn't see anything about being allowed to take the deduction in a different year than the donation year.
Pub 4303 referenced another Pub about appraisals. It looks as if CarMax is a valid appraisal in this instance.
I ended up calling the charity seller because I found their webpage where they announced the sale of refurbished autos and PCs. He had the sale price handy and it was above the CarMax offer and the dealer sales. It's a crazy market for used cars.
In order to file, I need his signature on Form 8453. If I don't get his signature, the max that can be deducted is $5000. School is actually in spring break, so it looks as if I'll be filing for an extension.
