Here are couple of diagrams. The first two come from "Die Armbrust" by Egon Harmuth. The other is form Jens Sensfelder's "Crossbows in the Royal Netherlands Army Museum".
It is important to note the fundamental difference in the action of these two locks. The difference resides in the interface between the tumbler and the intermediate lever.
In the first lock, the working faces are "square" to the axes of the two parts. This interface is stable, and will hold the energy of the bow without further assistance until the rear end of the lever is lifted. In this case, it is lifted by being knocked up by the set trigger, but it could just as easily by lifted by a simple trigger.
In this sort of mechanism, the energy to overcome the lock must be supplied by the trigger.
In the second lock the working faces of the tumbler and the intermediate lever are "oblique". They form a sort of ramp. and the tumbler is always trying to escape. The rear end of the lever must be locked in place by the "square" working faces of the trigger.
In this sort of mechanism, the unlocking is driven by the energy in the bow, and must be held in check by the secondary locking faces of the rear of the lever and the trigger.
If this is already obvious to you, I hope you will forgive me. If this is new information, I am sure you will realize its importance.