Hmm... no, I just looked at the confirmation e-mail, and it was definitely D005927, which is the same as the code in gnaget's post above. But it works. Shows up as "corporate rate" in the reservation, with no more detail.

I also just spoke with my dad, and he reports that the guy at the Avis counter was really impressed with his rate when he picked up the car yesterday. Luckily the guy was impressed in a "wow, great rate!" kind of way, not a "hey now, wait a minute!" kind of way.