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My experience is limited to sidelocks, and all of them have a second independent intercepting sear with a lever, operated by the trigger, to trip the sear.

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What sort of action or sears do not share this function? What sort of guns or rifles are they found on?

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JPK,
Do you have a copy of Grey's book, The Hammerless Double Rifle?
If so take a look at page 68 where it has some details on the H&H backlock mechanism.
It claims that the only way to fire the rifle when the tumbler has been caught by the intercepting sear, is to fully recock the lock, which of course would require breaking the gun.

Also if you have Greener's Book, "The Gun and its Development", look on page 208 where there is a diagram showing the Scott's Automatic Intercepting Safety System.
This type of interceptor allows the tumbler to travel most of the distance toward the striker before catching or blocking it's (the tumblers) fall.
With that system the lock has released most of it's energy and the gun would certainly need to be brought back to full cock before that barrel could be fired.
It also appears that no amount of trigger pulling would be sufficient to release that interceptor once it was engaged.

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