Italian library is pretty much a jungle about the issue. I'm sure there are quite a lot of of tracks, recorded for a library and never released. Both because they've been lost or forgotten under piles of other things, as I've recently read in a interview to Umberto Santucci. If I recall well, also David Nerattini aka Little Tony Negri (Pinball Music, Flipper Music, Penny Records), has talked about this somewhere.
Most of times we don't even know of their existence, till some indipendent label brings them to light, as recently happened with Afro Discoteca from Alessandro Alessandroni at Four Flies Records, for example.
Or again, the even more recent "Lost & Found", always from Alessandroni, on Four Flies.
Quoting:
"This EP contains unreleased music composed and produced by Alessandro Alessandroni in the 70s, taken from a dusty tape found in his vault".
"All the tracks were previously unreleased and are presented here for the first time - a truly "Lost & Found" treasure that sees the light for the first time!"