I have a Limited and am doing this from memory just from when I was looking for places to mount a ham radio display.
I don’t think several of the holes are seat securing bolt holes on top for most of the seat configurations (in terms of keeping the seat in place). There’s a bolt on the side of the rail that actually attaches the rail down to the lower assembly, for most of the corners, as I remember seeing them and trying to determine if I could slide a mount attachment point between the bolted pieces. I believe the ‘inwardmost’ rear connection point of the front seats is a vertical bolt into the subfloor but I think the alternate corners have a sideway bolt, and the holes on top are for a variety of different cable harness retention points, etc. I know on at least my passenger seat the top rail holes were either unpopulated or unthreaded and just had a cable retention snap in place.
Should be different between seat configs between trims, resulting in unused holes. I’ll have to look at mine, but I don’t even think there’s any threaded fitting beneath the hole on the top of the rail on multiple corners for a bolt to go into. My seats are absolutely rigid with no play.