I just found a CA 1910 12 bore , grade xiv, with a skeleton butt plate, the first Sauer I've seen with this feature. Is this unusual?

yep...

Not really unusual but typically found on upper rung or higher echelon Sauer offerings.

Serbus,

Raimey
rse

I believe Griffin & Howe has had one for some time , but it’s an extractor gun.
Best regards,
JBP