Congrats on being almost finished with your BPG revision! A couple questions and suggestions.
First, I don't think the use you intend for AUDIENCE is an improper use at all. If you want something not to display, using audience="internal" is the mechanism in EAD for making that happen. Using altrender="nodisplay" might work as well. But the clincher for both is less a matter of what EAD allows (both approaches would be legal EAD encoding), and more a matter of what the NWDA system will actually be able to make happen. You can have all the audience="internal"s in the world in your finding aid, but if your system can't recognize that attribute and strip out tags that contain it prior to rendering a file for display, your internal will be external.
For your filing title, maybe you could consider a way to get it into the <eadheader>, which most finding aid displays don't include anyway, so it seems like an easier place to tuck information that you want available for indexing or list generating, rather than for display. <notestmt> is a nice open-ended place to stash things like this. You might also use the <?filetitle ...> processing instruction approach (just before the initial <ead> tag) that the OAC uses. But again, how you approach this is completely dependent on what the system that is processing and rendering your EAD-encoded finding aids can do.
As far as local topical subject terms, the OAC used to tuck local California Digital Library terms that were needed for the CDL Directory into <notestmt>, which worked fairly well. If you are going to use these terms to help NWDA end users get access to your finding aids, though, I guess I'd wonder why you want to hide these terms from end users? Why not just make it easy and display these with the rest of the <controlaccess> terms used under some heading like "Northwest Digital Archive Subject Access Terms"?
| Bill Landis
| Manuscripts Librarian, Special Collections and Archives
| The UCI Libraries, University of California
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