Hi David,
OK, Finsbury Park is a particular problem at the moment thanks to the coronavirus one-way system and the special setting on the gates to platforms 7/8.
The station has what’s known as an EOSI set which means that an attempt to touch in within 45 minutes of a touch out will result in the two journeys being combined. This is needed because the validators at the exit from platforms 1/2 are actually part of the Underground station even though most people using them are Great Northern passengers. The journey needs to be joined so that when people change to the Underground (after walking round to the other entrance) they are not overcharged. Unfortunately it does cause a problem if the return journey starts in under 30 minutes after arrival.
Now, in normal times it is possible to get from the Underground to National Rail without touching out. To avoid problems the gates to platforms 7/8 are set to continuation entry which means that if you are already in the system you will be allowed through. This touch is recorded as a pink reader because it is a single intermediate touch. All this came about because of the lack of coordination between TfL and First Capital Connect. It will only be resolved when gates are installed at the bus station entrance to the National Rail station so that the whole station is gated.
So, when you were charged an incomplete journey it was because you tried to touch in too early for the EOSI and you ended up with a circular here-to-here journey from your Great Northern station. I don’t know why you were undercharged on the most recent journey, but I’d keep the pennies as compensation for the inconvenience with other journeys. If you can copy the expanded journey history here then I’d be interested to see what happened.
Finally, First Capital Connect no longer exist. The National Rail station is run by Govia Thameslink Railway (GTR).
