The following piece is often
used as "proof" that Weiss used the ring finger:
Ex.1
At the first glance it certainly does seem to be conceived as
a typical arpeggio piece we might execute on the guitar with
a-m-i-m for the melody line.
However, we just happen to have a fingering in an addendum to
a hand-copied version of Le Sage de Richée's instructions
found in Ms.Wroclaw 2002 which suggests the following fingering
for exactly this sort of passage. It is called "an example
of good and proper fingering":
Ex.2
To be fair, I should mention that all of the other examples in
this addendum involve the use of the ring finger, mostly in arpeggios
of four voice chords, but all starting with the bass. I'll post
the entire page as soon as I can get permission from the American
Lute Society to reproduce it. It can be found in the LSA Journal
vol. IX, I think from 1976, in an article by Peter Danner and
Doug Smith: How beginners should proceed (The original is in
German and would copy badly.)
Also known as the Kniebandl ms, Wroclaw 2002 contains works from
Weiss and Kellner as well as a certain Weiss Junior. Many of
these pieces can be found on the website of Michael
Treder.