Funny, I had pretty much that problem with HTs when I grew them on Dr Huey rootstock but did not spray for blackspot. What would have given away the game for me would have been if those same six inch tall plants were immune to BS. Still, I'm staying well clear of J&P until they get their act together.
I'm almost constantly surprised by how roses that have been in my own garden for a while look under slightly different conditions. Abe Darby's and Baronne Prevost's roses look markedly different season to season and through the season. They can also look quite different place to place. I planted Gemini this spring. When it was blooming I had no idea which rose it was. I had to check my planting records. Gemini looked so very different in my NJ garden that I did not recognize it here - and it wasn't entirely due to the lack of black spot. The flowers were a warmer pink, less mottled, and had more reflexed petals. Finally, I expected that sometimes Double Delight would resemble Cherry Parfait when I planted them near each other, but on a rare occasion, I have do a double-take before I figure out which is which.