Well, sure, but the doll's head per se is not a third bite.

The Rigby-Bissell rising bite is.

A third bite is generally considered to strengthen the doll's head or whatever rib extension is used.

One would expect that to be an advantage on double rifles where pressure is significantly higher than shotguns. But having said that, third bites are not uncommon on higher-grade shotguns as well.

...and maybe on more modest-grade guns too of you regard the Greener cross-bolt as a third bite!