I am not familiar with dog locks at all. Had assumed the mechanism fired by the trigger moving the external lock out of the notch in the cock. So it now appears the function of the dog is to serve as a safety with the tumbler and sear functioning as in a flintlock? Is this correct?
It is just an external safety catch. To apply it, half cock the lock, then pull the cock back slightly and engage the catch. When engaged, the cock is held slightly back from half cock, but the tip of the sear is still in the notch. Draw the cock back to full cock, and the dog is automatically shifted clear.
There are "English" locks that may have dog catches, but use lateral sears which engage the tail of the cock at full cock, not the tumbler.