Spotted a sheet of paper in the Gold Booth at SAN relevant for Platinum members, it read:

Platinum Assignments
A6, A, B, C=F
D, F, G=I
all other classes=car booked


Any thoughts? I imagine it works like this:
Book A6- Manager's Special, A- Economy, B- Compact, or C- Intermediate
Upgrade to F, full size

Book D- Standard 2 Door, F- Full Size, or G- Premium
Upgrade to I, Luxury

This might be for SAN only, because the paper was pinned to the wall and didn't have any Hertz markings, but it seems like a guide for Gold agents when Platinum members ask for an upgrade. This is the first real evidence I've seen of guidelines for Platinum's hard benefits. If so, PC seems to capture most of the same upgrade scheme up to Premium cars, given the difference in car class prices is fairly small and you could just book an ICAR for a one-car class upgrade to a FCAR.