I asked my question out on Facebook among the various PRR modeling groups and the consensus was that the late 40s version would have immunization imitation gold leaf lettering and the 50s version would have buff lettering. Based on that information, I pre-ordered the 1950s version.
I probably didn't need the 5-pack as I already have three BLI P70s, but fortunately the road numbers don't overlap.
More and more I've been daydreaming about a more permanent N scale PRR layout in some future house back East that would have sufficient size and trackage to justify a much more robust roster. It would have scenes from both the electrified territory and the Middle Division to Altoona, some prototype and some freelanced. I figure under than scenario, there's room for lots of P70s!