Thank you very much for clarifying this for me and in such a timely manner. I really appreciate it.
My mental model was that I would right click on the photo and then choose which catalog to remove, which was the wrong model.
Now I understand, you select the catalog in the upper left using the checkbox and then the operation applies to that catalog. So to remove from catalog A, if in both A and B, you use the modify checkbox for only A, and then remove.
Thank you very much, worked like a charm.