What are these holes in my Suburban door for?

[Old Bleu]

RoyL, I have the same problem on my driver side door. Someone bondo'd the original holes and mounted a car mirror farther back. The good new is that the original holes are still visible through the finish, so I hope that I can use a small drill bit to drill through the bondo and then run a tap through the holes to clean them out. The passenger side has never had a mirror mounted, but does have the backing plate. I think I will try your center punch trick on that side since I have a small spring loaded center punch. Of course then I have to fill the car mirror holes...