Because <fn> elements with IDs don't generate content themselves, I keep them self-contained inside the table that references them. This way, they move along with the table if I copy/move/conref it to a different topic.
Are you trying to validate that all footnotes are used, and none have gone silently unused?
Is this check going into a Schematron file, or is it being put into some other XSLT file?
