Quoting from the donor's e-mail, his collection consists of the following:
Carlo Albinessi, Arensky, Sterndale Bennett, Blumenfeld (I have his complete piano works) Busoni, Chaminade (I have her complete piano works) Czerny, Robert Goldbeck, Stefano Golinelli, Gottschalk, Granados,Grunfeld, Heller (I have quite a lot that is not on the site), Henri Herz, Richard Hoffman, Hans Huber, Alfred Jaell, Halfdan Kjerulf, Kopylov, Korestchenko, Liapunov, Martucci, Poldini, Raff, Reger,
Henri Rosellen, Anton Rubinstein, Saint-Saens, Julius Schulhoff, Ludwig Schytte, de Severac, Smetana, Nicholas Stcherbatcheff, I have Turina's complete piano works, but that one needs to be watched. Rudolf Viole's Eleven Piano Sonatas, Wihtol, August Winding.
Also, he mentioned these because he knows the birth and death dates of them (and hence the listed are in the public domain), meaning that there could be more...