I was in touch with Jack Richardson a 10+ years back before he passed - odd bit of serendipity where he was a professor at a University a friend of mine was attending. I asked her to give a letter to him and he responded! (I'd completely forgotten I still had his letters until I was cleaning up the other night!)
From his recollection, the early Guess Who Quads (Wheatfield Soul through Best of #1) were mixed by him and several members of staff at RCA. He mentioned it was his input as producer that kept the early ones from being 4-corner discrete. He didn't like that method of mixing. However he was told later on that these style of mixes weren't good with CD-4, and after CD-4 became the format of the day, somehow or another RCA chose to put another person in charge of the actual mixing. Mr. Richardson wasn't pleased over the decision but since he had no idea what CD-4 was or how to mix for the format, he conceded to the RCA staffers.
#10 through Power in the Music were all mixed by various folks at RCA studios with little to no input from Jack or the band members. Artificial Paradise isn't just double stereo. There does seem to be some minutely discrete moments but the rears are clogged with heavy delay. Flavours and Power in the Music are most definitely double stereo. Mr. Richardson could offer no explanation for this other than general malaise at RCA for The Guess Who in the mid-70's. At that time he said the multitracks are most certainly surviving, so in the 70's, RCA would've had no problems accessing them. It was probably an effort to put out product to fill shelves but put in minimal effort. Why Artificial Paradise is such a mess is anybody's guess.
When I asked him why So Long, Bannatyne wasn't mixed (as it's probably my fave album from the boys) he claimed it was "time". SL,B was a long album and there was a 40-42 minute limit on Q8's. I asked if it was attempted and he said YES it was, but mixing was abandoned when they learned of the time limitation. The mixes from that aborted Quad album were eventually used in Best of #2. Live at the Paramount suffered the same fate.