I was getting confused. BBC Select did indeed start in the nineties, it was the Discret service for doctors that started in 1988:
https://www.newscientist.com/article...bscription-tv/
I agree, it does seem unlikely that the cable companies offered these services, presumably meaning that cable customers wanting to use them had to somehow insert a decoder inbetween the analogue STB and their TV.
If this wasn't technically possible, they would have had to pick up the analogue TV signal independently of the cable signal and decode it in just the same way as other ATT viewers.