It is a little confusing having 2 tags for the Age of Empires II game (one for the HD release). There doesn't appear to be a running theme for other games that have been "re-mastered" or "re-released".
Related to this unanswered question: What to do with reworked/remastered games?
In regards to the situation with Age of Empires II, we have questions in the age-of-empires-2 tag that would also be relevant to the age-of-empires-2-hd tag but are marked as age-of-empires-2 only. For example, several questions regarding online play (where to play, lag issues etc) that don't always include the age-of-empires-2-hd tag.
The key difference between both games is really down to the Steam features/platform. Nothing in-game (campaign, units etc) is different, with the exception of the Forgotten DLC (although this started as a mod on the original game).
Would it not be better to simply merge age-of-empires-2-hd into age-of-empires-2, and for any of these merges also add a steam tag if it is missing (not missing in all cases)? For the purpose of people following the tags - do they really need to follow 2 different tags? What purpose would there be to only follow 1 of the 2 tags?
Look at the Monkey Island vs. Special Edition release. The game has one tag, and you can clearly see the questions that are specific to the SE version by scanning through the questions. Same goes for Half-Life 1 having 1 tag, despite the game having arguably 3 different versions (original disk, Steam release and Source release).