If there were earlier mainstream digital recordings they would be known about. In the late 70s and 80s record labels liked to make a big thing about their vinyl Lps being from digital recordings because people were pre programmed to think new tech meant better. A mass of secretly recorded to digital rock records does not exist. In fact many engineers clinged to analogue as long as practically possible, some until hi-res digital was available. I'm sure at one time I was impressed by a digital logo on an LP. That was before I heard early CD playback and realised digital was not all that was claimed of it. I believe quite a few digital classical LPs came out before Bop Till You Drop. Classical enthusiasts lapped up everything digital. Quite a few recordings employed some form of digital mixing from analogue tapes and of course there is the unsubstantiated belief that from later 70's digital delay was used in most cutting chains making most records digital.