I'm not sure when it was shipped, but the box shows it was made in July of 1990 (which is more in time with the square trigger guard). And as for parts, about the only ones it has in common with a 669 or a 6904 are a few pins and the magazines. Your gun has a proprietary slide and frame, as do all the early DAO models with the half-cocked hammer. It could not have been made as a transitional parts gun.

Now, there is a very good chance that this lot of 512 were made in 1990 and sat around the factory for 2 years until they were shipped off as part of a deal with RSR.

I remember handling a 5944 dealer sample way back when. Nice.