That's been my hypothesis too. And I think we can safely discard the idea that the rivets are left over from a prior owner.
Alli know is, if/when we get this all nailed down and I (finally) do my ANH conversion, I'll be dropping a wood plug down the bottom tube and driving all the rivets into it.
It only makes sense. It’s too coincidental to have TWO flashes which had rivets added for some unknown reason in their first life, or two flashes (three, including the Elstree) which were abandoned attempts at a motorized FX.
Also, I have to ask...how sure are we of the timeline for the publicity photos? I was not entirely convinced that any or all of them were post-production (except, of course, for the Bob Seidemann stills). Is it possible that they’re pre- or early-production, and that the second set of rivets was added to the toe pic saber during location filming? The “new” set of rivets does look bigger than the ones we already knew about. Maybe they were an emergency, on-set addition.
Or, perhaps the toe pic saber was designed as more of a close-up hero, with only one set of rivets (which would be less obvious, especially given their placement on the usually-unseen side of the prop), and the Tunisia saber was built to be a little more rough-and-tumble, and less pretty for the movie camera and the publicity stills.
We need more info, but the Tunisia prop is presumably hanging backwards (clamp facing him, rivets facing out) on Hamill’s belt in the photo, compared to how it usually does (clamp facing out, rivets facing him).