Interesting Mike! A brief version would be 'PP & JP in the USA!' I'm sure Percival and probably the RAF would've flown PPs and JPs together, and I think the Shuttleworth Collection have flown their PP with the Kennet(?) prototype JP in the last few years, but I'm not sure. I suspect you'd most likely be right that it's a US first as both PP and JP are relatively rare and usually appealing to different owner groups.
FWIW, I'd suspect there's more than four PPs flying currently; there's at least one in NZ flying, plus the Shuttleworth Collection's example in the UK, and obviously the one you flew - but it may be that they've become rarer in the UK since I last was taking note; certainly we sadly lost one with a highly-regarded pilot only a year or so back.

Look forward to the jPpics!