I have a Hobbs double-sided grilegate custodial lock masterkeyed with compound levers. The belly has 2 different radii, each half the thickness of the lever, i.e. two different points on which the key step can bear. (Similar idea to masterkeyed wafers, but more difficult and expensive to make the levers, and cut the master and servant keys.) Sadly I only have one key for my lock, no way of knowing which it is.
Mine probably dates from 1930’s when the prison was built. The patent dates from 1922, according to UNION Encyc of locks.