Thank you for your quick response. The short answer, is that an illustrative example of the many text strings I am trying to exact-search for (using quotation marks) across multiple sections of a notebook is "int&prg#zz".
I am aware that non-letter symbols do not register in searches. But the search function does seem capable of finding this exact string within a page and intermittently across many pages too. For instance it has successfully found this string immediately after the string was first typed into a particular page. But strangely it fails to find it thereafter.
The wider context for this is that the Notebook concerned is built around a large OneNote database of coded topics. The main page features an index of tags for a very large full-text bibliographic database. This comprises more than 15,000 entries on a single main Notebook page, linked to single page entries for each specific topic..
Each tag on this main page is coded with a couplet of three-letter tags, joined in various permutations with the symbol '&' or digits '1' ... 'n'. For instance, the above tag 'int&prg' stands for the topic 'colonial modernity'. The tag is constructed by coupling the three-letter code 'int' (for 'international affairs') with the three letter code 'prg' ('progress').
Each of the >15000 tags links to a dedicated page in a different section of the same Notebook. Each of these pages is cross-linked by similar tags to other associated topic pages. When tags are used for these general cross-links they are preceded by a '0', so that all instances of a specific cross-link can be searched for in a discriminating way.
The specific type of string this query began with ('int&prg#zz') occurs within the text of a page, typically at the end of a line of text. Here the suffix '#zz' distinguishes such specific instances of this tag from the general links above, so that these can be searched for separately.
I could say more about the rationale for this database system if you like. It generally works superbly. But the present problem is odd, because a search for this kind of string across different pages in many sections sometimes works and sometimes doesn't. The same failure occurs across a large number of strongs structured in the same way as I describe here. I am unable to work out what determines conditions for success or failure.
I'd be very grateful for your help.
Yours
Andy