The Skeleton Butt treatment was a catalogued option for the original life of the Ansley H. Fox shotgun.
The pre WW-I Skeleton butts have a much larger area of steel at the heel --
Only picture I could find quickly, from
The Double Gun Journal, Volume Three, Issue 2.
while the later Ansley H. Fox skeleton steel butts look pretty much like Parker Bros. Skeleton steel butts --
From a late 20-gauge FE-Grade.