Query fav:user -sub:user alternative?

Hello, I see fav, -fav, and sub are available query metatags, but not -sub. I subscribe by artist and would like to see what I have in my favorites that is not from an artist I am already subscribed to. I did try searching and could not find an answer for this. Was there a reason -sub is not an available parameter? Is there a workaround?

Thank you.

Don't take my word for it as I have zero knowledge in the field, but I think it might be an issue with the number of call requests involving subscriptions, which is (I think) why subscriptions only update like once a day.

Subscriptions only store the most recent 200 posts. So even if -sub existed, after the beginning fav:user -sub:user would just show all your favorites, even if they're from an artist you're already subscribed to.