That's an index of deeds, and the distinction there is that "direct" is indexed by the grantor and "inverted" is indexed by grantee.

I don't think that's the same thing at all.

I think it shows quite clearly that your theory that Information Retrieval nerds just got confused/misapplied a particular kind of book index is inaccurate and that IR nerds have been around for longer than one might think.