I wasn’t really thinking of expansion liner notes, of the type Intrada and LLL put out with their releases, since I don’t really buy those any more. They can indeed be very thorough and informative. OST notes are usually a paragraph or two from the director, if that, and a bunch of promotional photos. In the era before wikipedia, forced to read whatever books on music my local library had, I learned the basics of music history, form, tonal relationships, and interpretive specificity from liner notes on classical albums.