In the Half Life 2 mod-turned-developed Valve game Garry's Mod, there are dozens, if not hundreds, of separate gamemodes, and to make things even more confusing, each server can have different modifications to those gamemodes. Because just tagging questions "garrys-mod" still leaves such a wide range of ambiguity (eg: hitbox issues in UCH, damage reduction of Kevlar in TTT, strength of barricade materials in Zombie Survival), should some of the more popular Garry's Mod gamemodes get their own tags (not all gamemodes require one, because of how many there are)?
This level of sub-tagging is not necessary. There are only very few games which have been tagged with additional detail, and these games (for example, TF2 - 427, Minecraft - 2545, Diablo 3 - 1997, Skyrim - 2502,) have hundreds of questions each.
A game with so few (27) tagged questions does not need a set of sub-tags.