The thread where these recent codes were discussed quite publicly on Slickdeals was recently zapped, so I'm guessing the SD effect flooded Avis with a lot of reservations, especially given how much better the pre-negotiated corporate rates are than the current market rates. As someone who normally books on Hertz or National they are much more clear when you book with a code that it is for a specific company (they give the company name) while Avis website shows nothing when you use an AWD (I mean, its an Avis Worldwide Discount). If I didn't know from this thread, it's very plausible someone just gets the code and books with no idea its not publicly available.

While the problem exists with all the negotiated rates across all the vendors, I hope Avis at least makes their booking process more transparent in the future. That doesn't mean some people will still book it anyway but at least then less excuse.