Or van Gelder is too old and/or hearing-impaired to be up to it any longer (he turns 85 this year after all), so they just take earlier CD releases, like the near-mono Grant's First Stand JRVG or the old domestic One Step Beyond, boost the volume, perhaps tweak it a bit, and slap the RVG tag on it. Perhaps an EMI bean counter ordered this practice in order to cut production costs. It would certainly be a lot cheaper.
I can't see what any other explanation could be. Saturday And Sunday was recorded after Frankenstein at the session, so you couldn't get this error by going back to the original master tape. It was only on those early CDs alternate takes were placed directly after their master takes, and the alternate take of Saturday And Sunday therefore came right before Frankenstein. There is no reason those tracks would be adjacent otherwise. And only those early JRVGs had near-mono versions of stereo albums.