I have fire formed many 220 Russian to 6 PPC. It works best if you establish headspace with the bullet at least engraved a bit.
Just because a case appears to fire form well does not mean that it does.
I very much agree that too much data is generally about right. Data, in and of itself, tells us nothing but lack of data may lead us to incorrect conclusions.
As a former short range Benchrest shooter I now freely admit to cleaning my barrels far too often. That idea came from the data from you...