[KLF] How rare is JAMSCLP1?

The whole thing with the rare cds got me thinking, how rare is the cassette version of 1987? I think I may have posted about it two years ago but don't exactly remember. I picked it up off some random website going off nothing but the description that it indeed was a cassette version of 1987 with a catalogue number of JAMSCLP1 for 10UKP and it turns out that it's what it was. Since then I don't think I've EVER see it pop up anywhere, is it really that rare? - Loki Ambrodious von Esling