Now that the trip has been completed I can confirm Mike at the SFO location took great care of us! The day before our rental I called up to check in and was ultimately forwarded to the location manager, Mike. He apologized for the error and explained that when the Corvette's were pulled they went through the bookings proactively to make new arrangements. However, since we booked far in advance they must not have gone back far enough and indicated when we arrived we would pick anything off the lot. FWIW, I did book 10 months early as it was our 10-year anniversary and I wanted to use points on a holiday weekend.
When we arrived at SFO, we met with Mike and he noted that against all odds, a Corvette was actually delivered a couple hours before our reservation. Nothing like cutting it close! However, Mike offered to stand by his word and offered us the Corvette or any other car on the lot! My wife went straight for a white 911. Instead we were walked over a couple aisles where a new 911 had just arrived.
Ultimately, we left with a 2016 Porsche 911 with 333 (yes, 333) miles on it...all for the cost of 6,600 points and $34 in taxes for our 4 day rental! Plus, we were given the Dream Car treatment and driven to the gate in a Town Car. While I cannot confirm this is "regular practice", in this case we were certainly happy and well taken care of!