The "ALL DLC" part of the keyword is both exciting and requires a bit of context. When v1.5.1.2s was released in December 2016, the game was still in its early stages. The DLC library was a fraction of what it is today. At that time, the "ALL DLC" would have included the base game (California) and a few early expansions:
American Truck Simulator (ATS) version is a legacy build from late December 2016 American Truck Simulator v1.5.1.2s -ALL DLC VR-
To be clear: