Hi Raf,
You are really good, I must say!
Although I was a teacher, and some members called teaching what I am trying to achieve here, this was of course not a test. You would have passed brilliantly though!
From my practical experience testing early wheellocks and matchlocks, some of the latter being in my own collection, I can tell that once it has been screwed in, that wing nut will block the sear from working on a mid-16th c. Nuremberg detached tinderlock mechanism, as well as on another Nuremberg ca. 1550 combined match- and tinderlock mechanism.
As these two tinderlocks are both so remarkable, I decided to dedicate to them a thread of their own.
As you correctly said, the lateral push button on early Germanic wheellocks after ca. 1525 worked as a reinforcing means of pressing the nose of the sear into the respective recess in the wheel; so it's more or less a sort of safety mechanism to amend the contact between the sear (nose) and the wheel when the latter is spanned. In other words, this safety mechanism acted opposed to a set trigger system.
I recall when the sear on those wheellocks was disengaged/released, you had to press really hard and the sear would be released making an astonishingly loud and hard-clicking sound! Wheellocks of that construction were favoured especially in Styria, where they were made from ca. 1530 to 1550 but in the Landeszeughaus Graz many wheellock guns of the 1580's and well after 1600 still employed the same archaic safety mechanism.
Best,
Michael