I never really considered them to be add ons until you mentioned it…….that is an excellent thought. There have been areas where the rivet was lost and they were replaced with a small nut and bolt with a rubber grommet to seal and protect. I have replaced those bolts with new aluminum rivets.
Well, there now, you have more confirmation if that's what's geauxing on. I mean, you have a rivet design, it's a great design. A design that's strong, smooth & sleek. A design many companies have adapted. It works well and takes a standard, finite system to employ. It works on all sides (bow, stern, bottom, benches, ribs, ... ) you name it.
Now, for what left wing, god awful reason do you believe it might be necessary to change that for such a crude, cumbersome, calamity prone option as a nut and bolt ??
No sir, i think you're correct. I think it's an addition by a guy w/ common sense and not the where-w/-all to install nice clean rivets at hand.