Why are post war preferable?
Sometimes it’s a matter of taste, in the sense that you prefer coated vs uncoated lens.
For me, what I like from each model would be:
530 - I prefer winding with right hand.
530 - Better viewfinder, usually cleaner because of the mirror coating deterioration of the 531.
531 - I prefer one ruby window only, this is when they added the numeration from 1 to 16 I think.
531 - Folding the viewfinder with one movement.
It’s gonna be interesting having the uncoated Tessar, the coated Opton Tessar and the coated Xenar at the same time.