Note that the slot between the 3rd quarter and the hour on the count wheel is deeper than the other three and that one of the lifting pins on the canon pinion lifts the release lever higher than the other 3. D = count wheel, C= locking plate, the others parts are for the auto-corrector. You have mis-identified the parts which is part of the confusion. An unusual corrector mechanism for sure, but only slowed me down for 5 minutes or so. I am not sure the pin which is connected to this lever and is guided by the slot is the right shape, even though that's what I saw on the other movement (picture above). The problem I have, is that the part with the slot which can be seen above the plate, lifts the pin connected to the lever coming from the right side to the warning wheel's pin, but not high enough so as to release the warning wheel. I assume the lever connected to the cannon pinion, in auto-correct mode, is supposed to lift the pin high enough to release the cam but not high enough if the pin is in the deeper groove (and thus only the slightly higher pin on the cannon pinion will do this, which will make the clock correctly strike on the next hour if it's out of sync). What I CAN see is that the detents for the first three quarters are shallower that the detent before the full hour chime. As the clock chimes the hour, when it ends that part drops, releasing the striking train warning wheel to complete the strike. The lever first rises and drops the snail, the rack is connected to a lever between the plates which releases the striking train, and the warning wheel of that train is locked by the steel part mentioned above. The strike is locked and release by the long lever that touches the pin portruding from the chime cam on the right and the little part that can be seen right above the center of the movement (steel).

Westminster chime full hour