1972 Upper Control arm question..

That's not a collar. That is a spacer.
The collars I have seen encircle the bushing preventing I don't know what, bushing walk I suppose.
The spacer is used , also IDK for what. But be advised that sometimes when you assemble these parts on the car and then tighten the cam-bolts, you may find that there is not enough thread up the shanks to put a proper squeeze on the goods to prevent the alignment from changing. My solution was to put thick hardened washers on, one under the head of the bolt; first item onto the bolt, and another on the other end on the outboard side of the cam. This puts the securing nut about 1/4 inch further down the shank into the threaded area. Now the squeeze will keep it in place.
If your spacer was under the bolt head, then that is what it was there for. I would like to use something wider there like a hardened washer, to spread the clamp-load. Your spacer could work, but I imagine it would bang out over time.
Well, I guess that spacer could just as easily be at the nut end.
And I should mention that this is only a problem with new cam-bolts. The factory cam-bolts did have sufficient threading up the shank. That may be why you find some bolts with the spacer and some without; the OEM bolts don't need the doctoring. If I am not making sense to you, just lay all your bolts side by side and measure down from the head to where the threading starts. If you find some that are not threaded as close to the heads as others; those are gonna be the trouble-makers, so they get the spacers.