Mr Thant wrote:

On 19 Nov, 21:47, David of Broadway
wrote:
But capping is valid everywhere that PAYG is accepted, which includes
both TfL and non-TfL services - including a portion of the OP's route.

But you are perfectly entitled to use the cap to get to TTK. What you
can't do is use it to get a discount on the long distance fare, which
is what not getting off the train amounts to.

I was merely replying to Mr. Anderson's suggestion that capping is a
special offer for TfL services. In fact, capping is available
everywhere that PAYG is offered, TfL and non-TfL alike, as long as the
entire trip is available on PAYG.
--
David of Broadway