Don't know if they're still there, but there used to be fragments of old models like the Stuka rocket carriage and the engine panels to a tank. There also used to be a CoH1 Puma model, and it even existing alongside the new Puma for a short time, but the model was removed from the files when Western Front Armies came out. In fact a few bits and pieces of old junk were removed when WFA came out, sadly I don't have any of it really documented, most of it was nothing anyway.
If you mean the Stuka Zu Fuss carriage and the rest of the vehicle models it's possible that they just refurbished the old models for the new game. One example to support this would be the replacement of the old Ost Panzer IV model that was "low quality" as in taken straight from CoH and just given a new texture, with the new OKW one.
So to me at least it's entirely possible that they just had the stuff laying around in the files until they were used and not needed anymore because they were fitted to the models since none of what you said you found in the files of the models were added to the game before the WFA.
Another 2 things were the addition of some USF units and weapons like the M1 81mm mortar before the Ardennes Assault expansion was released as well as the findings of the new USF vehicles like the Pershing and Calliope in the UKF Alpha.