As Adam said, the four titles in this release represent some incredibly tough quad mixes to locate, especially in Q8 form. The PPL quads were some of the last that RCA ever did, and Musicmagic is the VERY last Columbia single-inventory quad. It's tough to find a photo of the tape online, let alone a copy of the tape itself.
Jimmy Castor's Dimension III has never been in-print digitally anywhere, no rare Japanese CDs, no streaming, no iTunes, so this release represents its debut worldwide - its also another really hard to find Q8. The LP was one of the single-inventory QuadraDiscs, and you can find it because of that, but the Q8 seems really tough to find. It's also a really fun album - Castor is no Luther Vandross as a vocalist, but there are a bunch of great songs on Dimension III, almost the dictionary definition of a hidden gem in my opinion.
I think its also worth noting that Illuminations is the first of the Santana studio quads to be released in high-resolution, and as far as I know the first time this album has been remastered in stereo since the original Columbia CD release of the early 90's.
I worked really hard researching and writing the liner notes for all four of these titles over the last six months, and I know equal care has gone in to the tape transfers, mastering, design and packaging of all these titles. I didn't want to say anything until these were announced, but I hope its clear that Vocalion's scope isn't nearly as narrow as some people have suggested. Michael Dutton and everyone at the label are very passionate about quad so if you want more of this kind of thing there's one way to vote, and that's with your wallet.
One last thing I wanted to add is that I've been informed that the Return to Forever 'Musicmagic' disc is a short-run/limited edition pressing title so if you want a copy, don't delay in ordering. Obviously it's folly to suggest that something will be a collectors' item before it even happens, but given what the prices are like for some of the OOP AF titles now, it certainly wouldn't surprise me if the same happens with this one.
I wrote a blog entry for the label with more background information the albums that make up this release for anyone interested:
https://www.duttonvocalion.co.uk/vocalion-august-sacd-release/