I recently had a trip to SJC and used code A153710 as the AWD with ZW as the rate code.
I noticed that this was listed here before as possibly a corporate code and sure enough, when I made the reservation online using that code, the rate type listed it as 'corporate', so I made a regular ent.book reservation just in case.

The rates were almost identical,(about $55 for 3 days),though the A153710 was for a premium car while the other was for a full size car.

When I walked up to the counter,the gentleman mentioned I had the 2 reservations listed.
I told him I wanted the one with the premium size car and he processed it for me without any questions asked.