I can't really confirm anything yet but I think there are cassette releases for these albums as I've already found the cassette for Suite Yuuyuuki, but I've also found some points of interest for the other albums:
1: if you look at the back of the cases you can notice that there are 2 different prices, that means that it can be the more expensive price for the CD and the cheaper price for the Cassette
http://vgmdb.net/db/covers.php?do=view&cover=37022
http://vgmdb.net/db/covers.php?do=view&cover=60105
http://vgmdb.net/db/covers.php?do=view&cover=60109
http://vgmdb.net/db/covers.php?do=view&cover=1622
http://vgmdb.net/db/covers.php?do=view&cover=73211
http://vgmdb.net/db/covers.php?do=view&cover=7897
2: there are 2 different Catalog Numbers in the booklets however this second catalog number is not included within the booklet of Game Music Graffiti only the 2 prices on the back
http://vgmdb.net/db/covers.php?do=view&cover=48746
http://vgmdb.net/db/covers.php?do=view&cover=146470
http://vgmdb.net/db/covers.php?do=view&cover=37019
http://vgmdb.net/db/covers.php?do=view&cover=60107
http://vgmdb.net/db/covers.php?do=view&cover=60112
As I said I'm not sure if it is like this but if it is then it's a pretty nice discovery
the only problem is though that I can't find any sites that have these cassette releases for sale or stored which is pretty irritating