I do not consider a third bite in a doll's head to be a hidden bite. It's an small extension between the extractors and not very prominent, hence the term hidden.

A doll's head may or may not have a bite, but I do not count the doll's head itself as a bite. A bite (when engaged) tends to prevent the action from being manually opened. A doll's head without a bite does not do this. Note that I said "manually". Not quite the same thing as the opening forces applied during firing where the doll's head with out bite does tend to prevent opening.

A doll's head with a bite is probably better than one without, but one without will do as intended if properly designed and fitted. Greener used to brag up his cross bolt at the expense of the doll's head without a bite. The key to either is proper fitting. A Greener cross bolt accomplishes nothing if it is not properly fitted.