The most common US GOVT ACOG's that are usually stolen are in the following models - TA01NSN, TA31, TA31RCOM4 or TA31RCOM150
I dont think any of those are what you are looking at.
From the number of ACOGs, Aimpoints, and KAC sights being sold on eBay and at gun shows I do not think that they were all "stolen" but were sold in lots as surplus at some point. I have seen literally half a table of KAC rails, Aimpoints, and ACOGs at a gunshow that still had remains of camo paint and desert dust on them. That was not some Joe selling a few he snuck out the back door but probably a lot that was sold as surplus.
There are several factors involved with military equipment making it to the civilian market.
Supply and accountability went by the wayside about 15 years ago and within the last 2-3 years is being reemphasized as a command emphasis. There is A LOT of equipment that gets handed out to units through various sources. And a lot of that equipment never gets put on the books. Paper trails suck and people, whether Soldiers or contractors, are lazy. Or inexperienced.
Or there is excess and the supply sergeant does not want to do a FOI and add it to the books just to get rid of it.
And it's too easy to write off equipment, especially in theater.
In the end be suspect of any ACOGs (or at the bare minimum the standard issue models) out there. Ask questions of the individual. Talk to Trijicon. Are you ever going to be 100% sure? I don't know. But if you don't do your homework, "I didn't know" will at a minimum cause the loss of your optic.