Yeah, that would be clear thread drift. Maybe it's own thread?
I will go ahead and answer, though, assuming this will get split off with your question.
For a time after I started loading on progressives, I still used a single stage for load development. I do not any longer. Now I use the 650.
I do NOT weigh charges individually. I'm loading on the press that I will be loading the ammo on after load development. If I weighed out each charge individually, I'd presumably be skewing the test to more precise results than I would get in practice, which doesn't seem helpful. I want the test results to reflect the results I will get later.
I do NOT measure OAL on each cartridge. I could simply say it's the same as the first reason above -- no reason to skew the results away from what I'll get in practice. But in reality, I'm expecting some OAL variation. I do not seat off of the nose of the bullet -- ever. I always use the seating stem that makes contact on the ogive/cone. Since most variation in bullet length occurs at the nose, and I'm not pushing on the nose during seating, I fully expect that variation in bullet length to show up in variation in OAL, so checking for it is more or less pointless. I know it's there. My OAL isn't going to be perfectly consistent.