Thanks to Owen for much good stuff.

If authentickque fingering would have been such an issue in past times, we
would find more of them in the surviving music.

"Systems":
I'm suspicious of modern thumb-under fingering in early stuff, like the
virginalists. I hear it when someone uses it, the music gets another
texture.
In Bach, Scarlatti, Rameau or other 18th century virtuoso or otherwise full-
hand stuff, thumbs are necessary. I don't in the least think
about "historical" or not, I write what fits my hand and the idea I have
about the passage. It is a good thing to remember heavy and light, bar
hierarchy and the range of possibly appropriate articulations when deciding
about fingering.
But there is a limit: I used to play the sixteenth run in the c-minor Bach
violin sonata mvt.II, bar 4, r.h.: 32 32 32 3, to match the violin
articulation in bar 9, but I changed this after years for safety reasons to
543213 2. Possibly I'm now able to articulate this passage in any way I
wish, which definitely wasn't the case when I first played the sonata in
1986.
That sonata has some neat little challenges when it comes to fingerings!
[just look at II bar 30-32 r.h., or IV bar 34-37 r.h.]

In the allegros, I have typically four to six figures per bar written into
my part, sometimes less; often starting notes and the place of the thumb,
and everything that's different from routine solutions. Why would this be a
problem - people are different. I think I need this: I'm always very
nervous when performing and the written fingerings are my safety net.

But I would not go tell my violinist or anyone else that this is the Only
Authentic way to do it. Yikes


Tilman