You're right, Kay... The May Pang Tapes were totally unauthorized. May Pang had absolutely nothing to do with those tapes, in fact, she clearly distances herself from them.
The tapes were actually stolen from the studio !!!
No-one knows who stole the tapes, coz obviously, only very trusted people were allowed in the studio when Lennon was recording. So yeah, most guesses are that it was most likely a sound engineer.
The recordings were named 'The May Pang Tapes' coz they were made during the May Pang era (The Lost Weekend) and because May was producing Lennon's album 'Rock n Roll' from which the outtakes were taken. The naming of the tapes was a deliberately ploy to mislead people into who really released them.
Neither John Lennon, May Pang or anyone else knew the tapes had been stolen. It wasn't until they surfaced on the bootleg market the theft was realized.
It really is an interesting little story if anybody cares to read about the pirated/bootlegged May Pang Tapes: