I come to the conclusion there's something I don't understand about FM searches … by scrutinising .mif copies of existing .fm files, I have discovered a redundant style.
FM knows it's there – because saving the relevant .book as .pdf throws a warning about a missing font that's only used in this style – and admits it in the paragraph catalogue:
On the other hand, FM steadfastly the style denies exists if I search on Paragraph Tag (virtuously checking body pages, master pages and reference pages) in the files concerned.
Does Find Paragraph Tag actually mean "find paragraph tag as long as it's applied to some text"? That would be rather limiting.