Epping's long-term increase in passengers is probably explained by the fares policy, which puts it in Zone 6 whereas all the neighbouring stations on the Bishops Stortford line are way outside the Zones. Which is why Epping has a big problem with car parking capacity.
Marylebone is interesting, because although it has indeed seen a resurgence since Chiltern Rail took over 20-odd years ago, 1951 was before the Great Central line started to be run down in the first place. It would be interesting to see its figures for c1984.