What I think you saw was the Australian LP. The Australian pressing is CBS SBP 238022. It’s a gatefold sleeve with a separate printed inner lyric sleeve, so it opens out and has layers, which could easily look like a multi-disc set to a kid. The artwork has its own history. Tom Nikosey, who designed the 1984 poster, said his second painting was made for “the soundtrack double album cover fold out.” It looks like a double album was planned at some point. What shipped was a single LP in that fold-out sleeve.

Check the CD you still own. Look at the catalogue number on the spine and count the tracks. If it really has 20 or more score cues, that would be a genuine find, and I’d love to know the catalogue number and label. No catalogued release matches that.