Essentially the interchange bridges are solely for journeys made within Oyster/Contactless zone? If not, then you're out of luck?.
Someone from say Chatham buying a ticket to Rochester to bypass the barriers, catching the Thameslink to Abbey Wood before touching into oyster/contactless and carrying on on the Liz Line.
Or even someone not having a ticket for the leg from station X to Abbey Wood where station X has no ticket barriers (Stone Crossing/Higham)
I'm not 100% convinced by the logic, surely someone without a ticket, or with the wrong ticket could join Elizabeth Line without tapping in, and then use another wrong ticket at other end? I.e. there are still holes in the system....
In other news EL services will be impacted by the strikes next week. Apparently due to the need to get to and from Old Oak. Although no disruption until afternoon, not sure why?