I had a CURT A20 head delivered yesterday, waiting on the legs to arrive. Mine is also a universal mount since my truck doesn't have the factory mount system. Since I used to be an ASE certified mechanic before my back said, uh, dude, you can't do this no more, I do all my own work. I live by the ruleset, Trust, but Verify. I trust that they properly assembled everything, but I also verify that they did, especially given the way the condition of the packaging these things arrive in. First thing is make sure ALL the parts are there. Then disassemble the parts that are supposed to be able to be disassembled and make sure none of it got damaged in transit.
My new Curt was in some pretty beat up packaging, holes in the bottom of the box, plywood busted, but thankfully all was there. First thing I did was look at the assembly manual, then took the head apart to make sure it was still straight, and thankfully it is.
On the Reese, if it were my install, those caps would have come off, only so that I could see how they functioned and if they needed any lube. In that situation I would have been able to spot the missing cotter pins.
The one last step I do once it is in the bed is a pull test to make sure it is solidly connected to the truck. I want zero play, no movement at all. That is really the only way to know for sure that it is locked in place.
Since the mount in my truck was not installed by me, and has a Q20 in it right now, I know they towed with it, and trust they installed the mount correctly, but I will STILL Verify that all it properly installed and torqued. Why? Simple answer, my responsibility. Go drive a 80K pound semi for a living and you will find this will be ingrained in you.