This site gives an insight into just how much gates fluctuate over time, and particularly just how damaging that 2012-2019 period was. This is very apparent when using the compare tool - say Cov & Leicester - it shows we had a higher average in 60s, 70s and 80s (roughly the same in the 90s) and then things diverged massively. They really were dark times and the recovery has been remarkable really.
Link here: Football Attendance Database
Link here: Football Attendance Database