The Carole King Q8's are definitely an oddity.
Tapestry might as well be double-stereo. *IF* it truly comes from the multitrack and is discrete, it is the LEAST adventurous mix ever.
To my ears, it sounds double-stereo with some kind of compression or hard EQ'ing going on in the rear channels. Anything that appears up front is in the back, though maybe at slightly altered volume. It's also mirrored so that if something appears in FR, it also appears in BR.
Music is sure trying to be discrete. I believe it is, and the intention is to envelope you into the music, but it's done in such a fake, 1970's way. I think the intention was to try and surround the listener in the instruments but I don't believe the album was recorded with that in mind. So, rather than record a set of congas with four microphones on four tracks to capture all the subtle ambience, it might've been recorded on two, so to create two additional tracks of congas, they use EQ, compression, delay and echo to do so. Great idea on paper, not so much in practice.
Rhymes & Reasons is probably the best of all four albums, but that's not to say it's THE BEST. The mix suits the music. Carole is more up front on this one, but her vocals still follow up in the rear at a slightly lower volume and with some tasteful echo. Not four-corner discrete, but you can definitely pick out where elements are supposed to be placed in the area around you.
Fantasy is probably the most discrete and might even be trying to go for four-corner, Columbia style. I had to double check to make sure my back speakers were on though as the rear channels are very quiet. It's also a very front-heavy mix and there's definite use of the hard FL and FR positions.
The opening track seems a little unusual to me where it has Carole up front, her piano up front. These follow in the rear at very low volume. Bass in Front Center, Guitar hard Left and Conga hard right. There is NO TRACE of bass, guitar or conga in the rear.