With the release of The Desolation of Smaug, do we need multiple tags for the three Hobbit films? (I'm guessing that we do.) If yes, how do we go about retagging all the questions?
For the Hobbit specific movies.
For the Lord of the Rings specific movies
the-hobbit-trilogy For anything Hobbit related as a SERIES.
lord-of-the-rings For anything LotR related as a SERIES.
As Christian states in the comments to Tyler's answer, we should probably use:
I'm pretty sure that there's a meta post that states that we should always try to include the article in the tag name. We can probably synonymise the-hobbit-1, the-hobbit-2, and the-hobbit-3 to these tags to assist users.
I don't think that we have a policy on "trilogy" tags. They don't exist for questions about the Matrix or LotR trilogies. But we do have one for Raimi's Spiderman trilogy.