This may sound a bit daft but I'm beginning to conclude that the stud clamping screw is so much missing as intentionally omitted.
I currently have a 17J UT6497 in a Le Cheminant pocket watch and a 17J UT6498 in a Summit pocket watch, both from the late 70's/early 80's, and both without stud clamping screws. I was going to try and fit a screw to the 6497 as believed it to be missing, but recently acquiring the 6498 with the same omission suggested that it was intentional. Now this post convinces me even more.
It begs the question "why?", although the stud does seem to be quite secure in both cases. Thankfully neither watch is in need of any H/S adjustment else it would be more of an issue.