So D005927 is 40% now in Germany..... that's the same as the old USC code. Maybe the % varies based on various factors. A few years ago I used another D code, which was related to a small business conference. Suddenly the effectiveness dropped to around 10% from 30-40%.
It is easy to spot the discount in Europe. It's right on the contract.
Also, watch out regarding the use of codes in the US on weekends. Actually avis.com corrects it for you. I was renting in LAX with a very good USD 19.99 rate per day. Since there are no surcharges (off airport property?) in LAX, rentals are remarkbly cheap. However, the normal rate was actually 17.99, so the net amount with tax was around 20. On my contract the D005927 is not there and it was replaced by A888813. This might be the National Motorists Assoc code that I think I originally used when I registered with Avis Preferred. If not then I am curious how it appeared.......