The main problem was with the first box set (volume 1). Some discs were warped and visible damage. Also many reported that whist there were 7 discs in the box there were two of some discs and none of others. Don't think there was any specific pattern to which discs were affected. This applies only to the original issued numbered box sets. The set was reissued later, unlimited run, these had no box number and were OK.
As far as I'm aware the other three sets were OK.
All of mine including the un-numbered first set were fine.