Founded in the early XXXX as a manufacturing and distribution arm for the seminal and severe... [l155216], in various guises to enhance widespread public confusion, quickly expanded its research and influence with a further series of carefully crafted forays...

From Mystery Lab's official website:
Research & production for the Mystery (or X) Tape line took place mostly in the 2 decades from the early '70s to the release of the plunderphonic CD in late '89. Now, although this process is not yet finished, we have decided to celebrate the 20th anniversary of the Mystery Tapes International! (dating from the reversible reel copies of BurrOughs) mail order distribution service in an unusual way by making it even more difficult to get these tapes.

In the past it has been our policy to insure that the information about the tapes was obscure, while the process of ordering & obtaining tapes was to be easy & pleasant. No more. For the forthcoming period (of undisclosed duration) we will not tell you how to get MysteryTapes.

Also known as Mystery (X) Tapes: the John Oswald's cassette-only output & alias.

In 69 Plunderphonics 96, Oswald noted The distinctive feature of Mystery Tapes is their anonymity. We don't tell the listeners who or what's on them. With Plunderphonics we tell all.