Not great pics. Just some scraps still left, and a couple from my reference collection. Mid and late September at lat 51 UK. edit: Same plant. You can see it wants longer than our climate usually permits.
I have not done PM for a few years, but found it better in every way. I find anything coming down after the first week in October isn't worth smoking most years. Which was the problem for the RP.
I'm not sure what happens in October, but it might be Ca or P being drawn up and just deposited in the buds, unused. It becomes difficult to burn. Just hardening off and going black, if an extreme example. Sugars maybe? I don't know but it tastes like I could be smoking old bones. The RP was simply too late, and my partner (who chose it) that year held everything up further.
I have your critical sour going out for a test run this year. I'm about to start the mums.