I believe the missing piece of this puzzle is the rental market that occured between Aliens and Alien 3. When the weapons were returned to the company that made them after filming Aliens, the ones that were not stripped back down to core parts were rented out. I don't recall where I read this, but the brown bess was not a pupular color for the 'renters' as it did not "look military enough" so they were repainted before being rented out.
Then for Alien 3 they were just painted black over the top. Some time after that they were 'restored' yet again to get the black off. This is why the absolute "kicked to crap" look can't be trusted for "screen used" pulses. Sure they were weathered in Aliens, but the 'trashed' you see now in most present screen used pulses are a result of all the flip flopping of paint jobs, not an actual representation of what was used in Aliens
