This is another one of those inherently confusing 'multiple labels that are part of the same catalogue' things. From what I can tell, both Records PRD ('productions Régis Delaye'?), Discobole and Illustra-Son are essentially the same label, all produced by Régis Delaye ("Bernard Lamastre"). I don't think there were any other "Alexandre Kush" LPs, but Michel "Misha" Lobko has some LPs under his real name. Never heard any of them, though.
However, I can help with some info!
I'm fairly certain the first four digits of the catalogue number indicates production/release year and month, and the last its number in the overall catalogue
- e.g. IS 860 912 means "Illustra-Son, September 1986, release #12". As such, the two 860 9XX LPs are preceded by Discobole 860311 "Sound Illustration for Radio-TV-Cinema n° 11: Voyage en flûte" by Ida Heidel. I don't of the two LPs that follow these two (#14, #15), but they are succeeded by 870516 "Magic Music n° 2".
I'll just add - Illustra-Son seems to be the latest label name used, running from the mid-to-late-80's into the CD age. The label was even active well into the 2000's, but seems to have closed down/gone bankrupt a few years ago. Not sure if Monsieur Delaye is still around.