I just realized the missing piece of this puzzle:
For Standard Load (SL) Passenger Car tires, there are 3 possible pressures on the sidewall: 35 psi (where the max load occurrs), 44 psi, and 51 psi - the last 2 of which could be considered over-inflation.
So referring back to the page out of the Tire and Rim book (
www.barrystiretech.com/2005traloadtable.jpg), if the sidewall of a P225/60R16 were to say "Max Load 1609# at 35 psi", that would be correct, but it could also say "Max Load 1609#, Max Pressure 44 psi", or "Max Load 1609#, Max Pressure 51 psi."