The Tag name Started with a 1
(eg 87th precinct would be under 8)
Tags can be downloaded, exist inside the books OPF or you can add them in the Metadata editor. Since you did not do the last.... the book came with those. There is no reason you have to USE their tags.
Why would you put a tag for an existing (Calibre) field in tags? (Author, series)
You can use any section (some of these are data from standard fields) of the Tag Browser (the tool) to help construct a search
IMHO many tags are hold overs from paper card catalogs, where you made a CARD for each tag. Calibre can find any tag with a single search. (I hate getting tags 16 variants on 'Science Fiction' for a single title
) so there is no need.
(I also detest having a Science
Fiction book ALSO tagged as 'General' or '
Fiction'
) when it has a better tag already