Adco has been around for a long time and offered tons of stuff. I know they offered WOA barrels for a period of time and would do custom builds time to time. They were one of the few companies that offered custom stuff 20 years ago. I bet it's something that slipped their mind.
I had a few guns I forgot about when I moved my safes 6 months ago. Same goes for when I go through my parts bin, I have hardware and parts that I don't remember what they go to. I can't imagine moving as many parts as Adco does.