rossb, You've certainly thrown a monkey wrench into the discussion, if what you say is true. Can you cite some sources to support the idea that a mono LP derived using a stereo cutting head will react differently from a "pre-1968" or true mono LP (to take your own cut-off date), to the use of a mono cartridge? And what about modern mono re-issues of recordings that were made in mono back in the early 50s? (So the reproduction chain is: mono master tape to stereo cutting head to mono LP.) There's a lot of those around and more coming available every day. Presumably, the mono signal after a stereo cutting head is re-derived by re-combining the stereo channels, which are actually identical to each other.
You're correct, incidentally, about the Ortofon Quintet. The Ortofon website uses a lot of double -talk to make the reader think their mono cartridges are "true mono", but in most cases that ain't so.
You're correct, incidentally, about the Ortofon Quintet. The Ortofon website uses a lot of double -talk to make the reader think their mono cartridges are "true mono", but in most cases that ain't so.