On my last import, I realized that my copyright information wasn't being applied automatically. I don't know how long Lightroom has been doing this, but I need to go back and apply the missing copyright. Since there are varying years and a few different copyright owners on my past photos, I don't want to just blanket-apply a copyright to all photos, I just need to find the ones that are missing the copyright.
I've tried using the "Library Filter" feature on both the Text and Metadata tags, but 1) these are very oriented to data that is already there and not oriented to missing data (text filter), or, 2) don't include the copyright field explicitly (metadata filter).
I basically want a filter on "Copyright" that groups them into the various values of the field with one of them being "Unknown" or similar.
How Do I find Photos that are Missing Copyright Metadata?