Isn't the term "library cue" common for cues written to be re-used within a specific show, as opposed to "stock" which isn't specific to any show? Albeit the term "stock footage" does muddy that, since a show like Star Trek will refer to "stock shots" of the Enterprise.
I think they're different ways of saying the same thing. The library is the collection of stock items. You can have a stock music library or a stock film library or whatever. Library/stock material can be specific to a given show, as in
Star Trek's reuse of its own unique VFX shots, or can be shared among different productions, like the various cues heard in '60s
Doctor Who which were written for general use by the BBC. Sometimes material created for a single production becomes stock for multiple productions, like the way Franz Waxman's score for
The Bride of Frankenstein ended up being used in dozens of movie serials, or the way Ray Ellis/Norm Prescott cues written for
Lassie's Rescue Rangers ended up reused in TAS,
Shazam, Isis, and other Filmation shows.
In the case of TAS, we know original music was composed for the series, but there's no documentation stating that cues were intended to be reused again and again.
Do we need it? Given the limited amount of music, it's clear that it was meant to be recycled throughout TAS. And generally, if a cue was written for one episode and then reused as stock, you can recognize the scene it was written for because it plays out uncut and fits the action better than in its later reuses. (For instance, Ron Jones's score to
DuckTales. Watch the episode "Armstrong" and compare the music cues there to their reuse in other episodes. From the constistent motifs and the fit of the cues to the action, it's clear they were written for that episode, even though they were edited into scores for chronologically earlier episodes. In the same way you can tell by listening that the famous Gerald Fried fight music was written for "Amok Time" instead of "The Gamesters of Triskelion," say.) I've always been alert to such things, and I've seen TAS a thousand times, so I'm confident that there is no TAS episode like that. The music is clearly cut together from stock in every episode.
Besides, Filmation was a famously stingy studio. They reused everything they could.
Not to mention the way the TAS cues are structured. They're built around repetitive phrases that play on for a while and then either reach a climax or transition to another repetitive phrase. That's the very essence of generic library music, something designed to be cut as needed to fit any given scene, rather than something tailored to the events of a specific scene.