Hi,
GM stands for ‘General MIDI’ and it’s an old standard from the early 90’s which specifies certain things like patches and note numbers for tonal and percussive sounds in GM compatible hardware and software.
Toontrack drum expansions are GM extended, which means they are compatible with GM for the drum parts but utilizes the percussion range to extend the articulation seems available for the drum sounds. To simplify it.
If percussion parts would be included for GM in the libraries, it would limit them severely.
BR,
John