Yes, 376 is the last one known to have survived. In learning that I also learned that the published versions are materially watered down in their instructions and annotations, some of which, in the original, seem to be rather intimate.
Good stuff here. Food for research. Post more when you find it and I'll do the same.
Thanks.
p.s. what about the piano quartet. Do you have that?
p.s.2 Thal, any trascriptions by or of Fibich?