Hi @adigigo this is incorrect, the Piccadilly line operates in a one way loop via T4 so will always operate Hatton Cross ->T4-T2&3-> Hatton Cross with service to T5 operating Hatton Cross->T2&3-T5 and from T5 T5->T2&3->Hatton Cross
That’s not an error - the Terminal 4 loop operates only in 1 direction. T2&3 is a stop on the T4 to Cockfosters route, but not a stop on the Cockfosters to T4 route.
I believe that the reason it is still included is to aid with journey planning, so that passengers going to T2&3 aren’t forced to take a T5 train by the journey planner.
Cockfosters to T4 trains terminate at terminal 4 and then start a new trip, so if T2&3 wasn’t included, then anyone using open data would be under the impression that one of these trains cannot get you to T2&3.
However, as passengers are able to stay onboard at T4 to continue on to T2&3, these trains are advertised with a destination of “T4 and T2&3” on departure screens, and T2&3 is included in the route so that journey planners also suggest boarding these trains.