I read 11.9 in the batch of stock I just made. As I said, it behaves just as I would expect Rodinal to behave. I don't think you need to worry. Just try developing a test strip. The diffrence between 11.9 and 12.5 is not much at that level.
I think from the standpoint of protecting the p-aminophenol, it is best to ddissolve the sulfite first, then the p-aminophenol, then the KOH. I think K salts were easier to get or make for the Germans at the time of Rodinal's inception. It was interesting to me that Hurter & Driffield mentioned rodinal, with the lower case, as a developing agent. I suspect that was potassium paraminophenolate. If that is available, it would simplify things for us, would it not?