The story/show/movie identification questions would benefit from tags designating the approximate era of the story/show/movie. It helps answerers find questions they're most likely to know the answer to -- I read a lot of stories while in high-school and as an undergraduate in the 80s but not so much in the 90s (grad school is time consuming) and none in 00s (kids are even more time consuming). Decades seem like the right range for 1900s, maybe 25 year blocks for 1800s and 100 year blocks before that? And (long-live SF&F-SE) it's probably better to have 1960s instead of 60s.
I doubt the necessity of decade tags.
While tags can easily be edited at a later date, I feel that tags should be used to definitively categorize questions with known constants/facts.
Decade identification is often too fuzzy in the memories of people. Just this morning, I was considering this question and trying to remember if the movie Shocker was from the 80's or 90's. I saw the film in around 1992 or 1993. At the time, it felt like a 90's movie, and I would have sworn it was from the 90's.
Sure, the question's tags could be edited if an answer is found, but that requires/involves extra unnecessary editing for the simple purpose of cleaning up tags. It makes more sense to me to just identify the possible decade(s) in the question.
I'd also question the usefulness of such tags. The intended purpose of tags is to categorize questions so that one can search or ignore questions. While some people loathe story identification or Doctor Who questions and might want to filter those out, or highlight them as favorite tags, I see little chance that someone would specifically choose to filter/highlight questions about works from any one decade specifically.
One other issue regarding the decade tags, is the question of which decade a work should be tagged according to.
For example: A story is written/published in 1985, but the story takes place in 2015. Which decade should the question be tagged with? Does one tag it based on the date the OP thinks it was published in, or when the story takes place?