Don't think we have in my lifetime have we?
I think we had around 19,000 for the League Cup Semi Final in 1990, very much a one off.... Arsenal we only pulled in 14,000 on the same cup run... So you are going back at least 26 years...
I think I remember a 18,000 gate against United around 1991? We had less than 19,000 when we got promoted to the top flight against Wednesday. We got over 18,000 against City as well. And there was a hell of a lot of City and United fans in the home ends.
20,000 ? Not in my lifetime I don't think...