I started collecting in 1979 and the top watches of that era; PP, AP, VC, Breguet all had solid backs, that's just the way it was. The great Patek Philippe's of that era like the Ref 2499 and 3450 had solid backs. Then about 1985, as prices started ramping up and more collectors appeared they started to want display backs. For awhile Patek Philippe, Roger Dubuis and maybe a couple of others included a clear and solid back in the package, but I don't remember seeing anyone swapping the clear back to the solid back. I don't care one way or the other, I seldom look at the back of the watch, I don't need visual confirmation that I spent my money well.