We have two tags, one for civilization-4 and one for its addon civilization-4-beyond-the-sword. This makes sense, as one is the original base game and the other is the version that basically most players are playing, as it's typically accepted as being a net positive upgrade from the original.
However these tags don't seem to be applied consistently. Some question about BTS have both tags, while others only have the BTS tag. Of course question that are about comparing these two versions should have both tags, but what about question that are only concern with BTS? Should they only be tagged with the tag of the addon, or should they also get the tag of the base game, as the addon is just an extension of that game? How is this handled for other games? Do we have an example for another game with a separate tag for an addon and how that is handled?