Update 17/10: Coninuation exit was apparently removed from the Kentish Town validators on 8th October.
As reported yesterday on the forum, there is a problem if you try to change trains between Kentish Town and Kentish Town West. Because the Underground station is closed, Kentish Town currently has no gates. Unfortunately the validators have the continuation exit setting so that if you touch one and then try to exit through the (currently closed) gates it doesn’t cause a problem. Continuation exit means that your journey will be kept open until you next exit through a gate or use a validator at a different station (or let the journey time out).
As an example, take a journey from Cricklewood to Canonbury. You touch in at Cricklewood, touch out at Kentish Town, walk to Kentish Town West and touch in, and finally touch out at Canonbury. Normally the Out-of-Station-Interchange (OSI) between the two Kentish Town stations will join the journeys into one. However, because Kentish Town West also has no gates, the system has no way of knowing whether your touch in there is really an in, or a further out. With continuation exit active it assumes it’s another exit and thus closes the journey from Cricklewood at Kentish Town West. You are then travelling to Canonbury on an unvalidated card and the exit there will be logged as an incomplete journey.
My advice for the moment is to avoid changing at Kentish Town from Thameslink. If you do need to do so you should touch out as usual, but when you get to Kentish Town West do not touch in. Your card is still validated for travel if continuation exit is set, and the correct fare will be charged when you then exit at your destination.
There is no problem in reverse because the validators at Kentish Town West will properly end your journey and the OSI will restart it when you touch in at Kentish Town.
I don’t offer this advice lightly, but if you are checked by a revenue inspector on the North London line you may be subject to a penalty fare or even threatened with prosecution. This is clearly not good as you haven’t done anything wrong.
The use of Kentish Town / Kentish Town West is required for some avoiding zone 1 journeys. However, as the Northern line station is closed, my advice now is to change at West Hampstead between Thameslink and North London Line.
Another data point on overzealousness of revenue inspectors on the North London Line. I have a full adult Z1/Z2 Annual Travelcard with Gold Card on my Oyster. They insist I need to produce a valid railcard when travelling within Z1/Z2. I have been fined 3 times so far this year, each time overturned on appeal. I’ve even produced the email from Revenue Protection confirming that I don’t need to produce a railcard, but to no avail. So my recommendation is that if you are admonished, don’t bother to argue, take the fine, and then appeal on the website – it will be overturned if you are in the right.
Is there a railcard discount associated with your oyster card?
The standard railcard discount includes the gold card, which is why they will be asking for a card. An annual travelcard comes with a gold record card which is needed to validate the discount on normal national rail fares. However, the prescence of the annual travelcard is visible on the Oyster card, so no further verification should be needed when using PAYG on the Oyster card,