Hi Michael,
Cuffley and Epsom are oddities. In both cases the stations are in zone 9, and caps/travelcards including zone 9 are valid, but the price of a Cuffley/Epsom to zones 1-6 travelcard season is significantly cheaper than the zone 1-9 version. Thus the zonal status of these stations is hidden. The fares are also set by different TOCs so there is no standard fares.
Amersham, Brentwood and Chesham fares are all set by TfL and there is no X to zones 1-6 option.
