It seems the shims which came with the lens were not correctly installed. The same lens was returned and was "tack sharp" when he next used it, said this was a common problem with the lenses. The glass was excellent, but the shims would normally be out of adjustment due to an improper c.l.a. or tinkering by someone who didn't understand the lens.
This seems to me to be simply a manufacturing issue from years ago. With today's technology and tolerances, the use of shims would be an unacceptable,costly and unnecessary manufacturing procedure. In the past, it was just a necessary part of the "system" for production. tim
In Mamiya TLR’s, shims are also used to align viewfinder screens... as a general suggestion, do not disassemble the viewfinder chamber, even if it is dirty. There is little to gain and a lot of risk to misalign the screen.