They did seem to throw details here and there for veteran Frictional Games players. Such as the Artifacts in the game that were similar to that of Penumbras. As soon as I saw those in Amnesia I immediately thought of the ones in Penumbra...and they almost do the same exact thing (except from another persons perspective and they dont save the game).
I wonder how many there are total, im pretty sure i found them all, but i didnt keep track of how many i found >< but i explored alot...or as much as i could without getting freaked out ><