That article points out an interesting problem. Single inventory quad being placed in the Quadraphonic section. I both loved and hated the separate quad section. On the one hand I would continuously check it out and even buy a few records that I wouldn't have bothered with if they had been only in stereo. On the other hand compatible quad releases weren't getting into the hands of stereo people, greatly reducing sales! An especially huge problem if the recording was single inventory!
It always really irked me when a clerk would ask, do you know that album is Quad? What! People are supposed to only buy stereo?