Original works by this person are generally still subject to copyright. Submissions of copyrighted works are allowed only with the permission of the copyright holder. In the US, all works published in 1929 and earlier in the public domain; works first published afterwards may be protected by copyright (with some exceptions). See public domain and the licensing policy for more information.
Theo (founder of Merton Music 1996-2010) was the absolute pioneer in the republication of forgotten chamber music, and I think it no exaggeration to say he was the IMSLP of the pre-Internet age. (from John Harding's obituary).
Merton Music 2009 catalog with its unique grading system, very useful for amateur chamber music groups.
The Merton-Ourtext Project at IMSLP enabled the upload of the majority of the Merton catalogue up through 2010, which can be browsed on this page.