asdf wrote:

If I am in the system, it's mostly likely that I got in at a place
where I had a valid ticket, and reasonable to assume that I did, and
charge me from the boundary.

No it's not. Otherwise, anyone with a Travelcard covering at least one
zone could have unlimited free travel anywhere where pre-pay is valid,
as long as they don't touch in/out outside their zones. For example, a
zone-6-only Travelcard holder could commute every day from Epping to
Waterloo (no barriers on the W&C), with no possibility of ever getting
fined/prosecuted.

Okay what if someone has a zones 2-6 travelcard and goes into zone 1 on a
National Rail service where PrePay *is* accepted, e.g. staying on a one
service beyond Stratford into Liverpool Street. How are they to touch in at
the start at stations with no barriers?

I don't think I'd touch at an open gate.

It's a requirement for using pre-pay that you always touch in and out,
even if the gates are open. It's certainly publicised well enough.

But it's badly publicised in regards the extension service (and the lack of
gates to enter the system at key points).

If you can't manage it, I suggest you don't try to use pre-pay,
otherwise you're leaving yourself wide open to being penalty fared or
worse.

So if I'm taking a single service that starts at a station where I can't
touch in through no fault of my own, and I use the extension facility on a
legitimate route, I am liable for a penalty fare for not doing something
that is impossible or me to do?