Currently, there are three tags for Plants vs Zombies: plants-vs-zombies, plants-vs-zombies-goty and plants-vs-zombies-series . Do we really need 3 tags for one game? Specially considering the low number of questions in the "goty" and "series" tags.
Are there important differences from the normal game and the GotY version such that it warrants value to separate the questions about them? Not just as far as existing questions, but what might show up. Consider the differences between just a patches and touch-ups (AoSX on PC versus PSN release, for example), a full expansion pack (Diablo II, Armored Core, etc.), and a sequel. If you're approaching expansion pack level of difference or beyond, then the second tag seems appropriate.
Are the two games then separate enough to warrant a series tag? If the GotY version is distinctly different to represent the sequel level of difference, then a series tag is useful. But if it represents an expansion pack or lower, then it basically inherits its features primarily from the original game.