There are three killflashes for the 4x32 ACOG, the original was much shorter, and was simply the "honeycomb" portion, Trijicon P/N TA57.
When the TA31RCO was developed, they also developed a new killflash that integrated a laser filter, with a killflash portion that unscrewed. This is what yours looks to be. For whatever reason, Trijicon did not, and to my knowledge, still does not sell the model with the laser filter to civilians, so most likely, what you've got there is probably a "bringback." For the reason you mentioned, killflashes are not necessarily popular with end users, and a lot of them end up being removed at the user level. Not a whole lot of sighting lasers and LRFs being used by the enemy these days. Like the KAC panels and panel pouches that sometimes get issued... accountability can be a little... dodgy when it comes to small, non-serialized accessories.
The third variation is identical to the RCO killflash, except it doesn't have the laser filter, but it does unscrew, it looks identical to the RCO killflash, and is sold both separately as the TA91, as well as with the TA31RCO and M150RCOs commercially.
So, yours looks, at a glance, to be an authentic RCO killflash with the filter intact.
HTH,
~Augee