They rarely reset tags individually based on the years of inactivity, they just reset groups of tags when the technical team feels like it. You can use the old halo 2 stats to determine last activity of the account but it is not always accurate as they may have logged in at another point of time. A lot of rumours are being said about MS not resetting tags anymore because of all the commotion it has called, but those are just HF trolls that are probably wrong.