I have the Mystery Discs and there is no MSX program at all on them. There is no mention of Palcom or MSX on the cover.
I don't understand how the game can be played/used though. There are lots of short scenes with a stop frame at the end. I'm guessing there are some instructions that say "if this happens go the frame such-and-such" but I don't have those.
What are those well-named Mystery discs? I know there were some board games in the 80's sold with VHS tape (mainly for instructions), maybe it's something like that ?