There is as of writing exactly only ONE demo for each volume, while the other volumes have many.
I think it would benefit VSL (in sale terms), to have more demos up for the latest volumes (3 and 4).
Otherwise potential buyers cannot judge the libraries enough on usability and/or sound design of the contents.
Be sure though that the demos ONLY use the library for which it is made, and NO other libraries at all. OR if you MUST use other libraries along the targeted volume, state so very clearly in the demo popup of the song, which library also is used (e.g. volume 1 and volume 2 plus) and which patches or sounds.
Just a suggestion :)