There are a number of tags that describe specific published books, mostly adventure modules for D&D 5e, for example there is one for curse-of-strahd, there is one for tomb-of-annihilation, and one for tales-from-the-yawning-portal (in addition to the published-adventures one).
In many cases (like in all the cited ones here), these books represent re-imaginations or compilations of much older adventures (here, of "Ravenloft", "Tomb of Horrors and "Dwellers of the Forbidden City", or of a number of explicitly referenced modules from first or second edition, like the venerable "Hidden Shrine of Tamoachan" or "Against the Giants").
When are these module name tags to be used?
Some questions are about specific 5e monster rules that appear only in those modules, like Does a Duergar Spy's Enlarge action double its damage dice from its Sneak Attack trait?, others are explicitly about that published book, like How "deadly" are the adventures in Tales from the Yawning Portal?. In these cases it seems pretty clear cut to be book-specific and warrant the tag.
Others however, like this one What are all the hints in Acererak's message? ask about features of the module (here a riddle), that are not specific to that 5e book, in a way that dungeons-and-dragons differs from dnd-5e: they are about that adventure in general, not about that specific book in which it appears. Still this question is tagged with the 5e book.
In the origial modules there often were idisyncratic rules interactions because back when then, the game rules did not cover these aspects in detail, and so writers made up ad-hoc solutions to things like difficult terrain. And in some cases, these aspects survive even in the current version of these modules, which may cause some more specific rules questions, like Does difficult terrain stack? where an alternate resulution instead of standard difficult terrain is used, in this case the question is not tagged.
Then there are questions are about some rule interaction that occurs in these modules, but it may be just a general rules question, triggered by running into it in the module. For example When is Passive Investigation used? askes about passive investigation, and only mentions the TotYP module in the introduction.
I have been rather liberal in adding the tag if a question mentions the book represented by the tag and there is unused tag space, even if the question is not explicitly about the book, because it seems to me that there actually would be exceedingly few questions that would hold up to scrutiny if one were to apply a strict measure and only tag questions that are about that specific adventure book given the history of many of these adventures, but maybe that is not the right approach. What would be good criteria on where to draw the line, what to tag and what to not tag?