Cross-London journeys: There is one other thing that you could clarify, which is not completely clear from the train company information, and (possibly!) from your excellent advice columns. There appears to be a hard and fast TfL rule that if you travel inbound to Zone 1 between 16:00 and 19:00, you pay the contactless offpeak fare if your journey ends in Zone 1. If your journey passes through Zone 1 and out the other side to any station outside Zone one, and you touch in between 16:00 and 19:00, you are charged the peak fare. Correct? The same rules appear to apply to Oval cash fares for mainline journeys.
I think the rule should be made clearer: if travelling in the evening MF peak, the fare paid is determined by the time that you touch in PLUS your destination station. The peak/off peak price differences may only be a quid or two on the Tube, but are substantial once you get outside London.
In some cases, it will be cheaper to buy separate cash tickets or use two contactless cards to optimise the fares. Eg Beaconsfield to Whitechapel after 16:00 would save £4.40 with two cards for two separate contactless journeys