So far, most of the same part number boxes have the same amount of total retard, but where the retard starts, and where it changes with RPM can be quite different.
Don't have my notes right in front of me because I'm working on a pair of tunnel ram carbs, but off the top of my head one box started to retard at 3100 and the same part number box didn't start until 3800. And both boxes retarded from there at different RPM.
I have no idea why that is. I may have to call Tuner and bend his ear and hear his thoughts.
Plus, I owe Tuner lunch, so when I buy him lunch I'll be taking notes!!!