Yes, usually, you must recheck your content regularly and check if old content validates for new tags, or if old tags have shifted in meaning, splitted into new

Yes, usually, you must recheck your content regularly and check if old content validates for new tags, or if old tags have shifted in meaning, splitted into new subtags, etc. But this does not necessarily mean you should check everything, and regularly must not mean every week or month. Just review small parts of your library for changes, occasionally as you have time, the improvements will come over time by themselves. A never changing library, is a dead library.