Online music libraries are totally new to me and this may be where my perceptions here are weak - T

Yes, that's probably why we didn't connect.

A film music library's publishing contracts can have an exclusive clause or a non-exclusive clause.

The exclusive clause gives the sole right to the publisher to permit advertisers, television, cables, radio, film, etc. to use the writer's tracks - with agreed upon compensation to its writers.

The only difference with a non-exclusive contract is that the writer doesn't give up ownership or the copyright of the master recording. The non-exclusive publisher will change titles of the writer's tracks, to ensure all royalties generated by their placements on TV, film, advertising, etc. will be funneled appropriately.

In a non-exclusive agreement, the writer still owns the right to the recordings, and can exploit his recordings as he/she sees fit. I have some tracks that are published by several music libraries (non-exclusively of course).

Bottom-line; both contracts are basically the same except for the exclusive/non-exclusive clause.