Shoooooo! What a snow job.

OSHA rules only apply if you have employees, not home owners or personal use tractors. All it says is the tractor must have seatbelts--
For employees. And it only means something if the employee/driver actually wears the seatbelt. Have you actually looked at a ROPS? I mean a factory ROPS, not a CROPS or CRAPS more like it. The CROPS are full of un-backed holes. I've included a pic of one of the CROPS you note below.
My factory ROPS came with "engineered holes" and there's no internal backing. And yes, it has a label attached. Hard to tell (signs of welding) in the video if there's backing since the paint job is so bad but I'd be willing to bet there isn't. One way to tell if there's factory backing is to put a bolt through it and start tightening a washer and nut on the other side. If you see the wall(s) start to deform, STOP. There's no backing.
I'll be using "pass-through tubes" at my factory top mounts to stop the compression. Mine are factory 1/2"+ holes so I'll use a tube through each hole with the bolts passing through the tubes and the ROPS. The compression force will be applied to the tubes, not the walls of the ROPS.
Incidentally, my new lawnmower came with holes in the ROPS and it doesn't have backing behind the "engineered holes" either.
View attachment 696292