As a collector of early recordings- 78s and cylinders are quite fragile. In
my opinion it is quite possible that even 'many' MT recordings simply did
not survive.

I owned a very rare, expensive 1905 one-sided disc by Ossip G's friend Mark
Hamburg, who also attended the Vienna dinner where O met Clara. It cracked
one day as I picked it up with two hands. Early recordings were discarded
when broken. They break even in protective albums. Cylinders decay. Empty
cylinder boxes are common in antique stores.

I have also never found any trace of Clara recordings, having visited the
Berkeley, Hartford and Detroit archives. I would be very surprised that she
never made home recordings, speaking as a vocal coach. In my extensive files
on the Gabrilowitsch family, no hint of a Clara recording.