No, that's fine mate, but I would just like to add that there is a big difference between what many would refer to as a "third fastener" and an actual "third bite". The latter implies that the doll's head is 'bolted' when the action is closed. A Doll's Head might be regarded as a third fastener in its own right, and it will add strength to the lock-up for sure, but a doll's head with a third bite is much stronger. A Greener Cross-Bolt is an effective third bite too, and one of the best. Also, the Purdey-style 'hidden third bite' is a third bite without a doll's head or rib-extension

Both these doll's heads have a third bite:

And just for laughs, here's a German double rifle with a Greener cross-bolt and a doll's head!