*If* a Travelcard holder starts a journey and validates their card at a
station outside of their zonal validity then there will be a deduction
from their PAYG purse of £1 (starting at an origin in Z2-6D) or £1.50
(starting at an origin in Zone 1). At final exit the gate or validator
will determine if any more money needs to be deducted from PAYG for the
extension journey.

I know I asked this before but there was confusion about the answer. I
still don't understand what happens if you have a Travelcard (on
Oyster), touch in within your zones of validity but are unable to touch
out at the destination.

Specifically, I am referring to the large number of people (myself
inc.) who have to touch in at Ealing Broadway (Z3), take the overground
to Paddington but cannot touch out there. How would the system know
that I didn't take the tube outside my zones of validity and failed to
touch out at the arrival station (and should therefore have a fare
deducted from my PAYG)?

Jase