I haven't find any 88 P yet. We mostly received (D) mint here at my location (Bay Area San Francisco). (P) mint are rare here lol. And most of the good stuff come from the other side of the country lol.
I believe in this case as far as value the 88 D carries a higher premium than the P but in a whole there do seem to be more flub ups at Philadelphia especially when talking about transitional varieties.