(17 Apr 2019, 4:49 pm)Andreos1 wrote It was clarified that Boundary Houses was the red zone border the other day. 
The section beyond there to Bournmoor/Woodstone Village is within the green zone. Beyond there, the 4 goes back in to the red zone.

I often used a T&W ticket (it was much better value than the Day Rover at the time) on the 21A, despite it heading in and out of Co Durham. 
Unfortunately both the ticket and service were culled.

As far as I'm aware the 4 has never been included in the green zone. The route map on GNE website states red zone after penshaw bank top. Yes it goes to green zone as soon as you turn off to woodstone village (the zone change for the 36/78) but not going through burnmoor and fencehouses.

Perhaps people are getting confused as the T&W area ends at boundary house and restarts at the fencehouses rail crossing (hence the lack of nexus bus stop timetables) GNE allow network one tickets to travel through county Durham on this part of the route without paying extra