How to search for Rems that are disconnected from the rest?

I’m doing a cleanup of my knowledge base. I want to search for all the Rems that are not tagged or linked or appeared in a portal or nested as children of any Rem. Is there any good way to do this? I am aware there are tags like Stub or Orphan but they don’t really capture these disconnected Rems because of the circumstance these rems were created (after importing some document, odd things happen)