How do I compare two observing lists?

[derangedhermit]

i do make use of the Observing Lists tab in Object Info; it is a nice feature that enables manual screening.

I also do the merging of two lists as you (very clearly) describe in your steps. I had not thought of using checks prior to merging as a way to identify the new unique items. That will be a real timesaver. And as you say, I can do it twice, once to find what is in both A and B, and in B but not A, and once again for A but not B.

Thanks,
Lee