Forgive me as it is a bit off your topic, but a similar situation made
me wonder when I was to London last week.

I had a 7-day travelcard for zones 1 and 2 on my Oystercard and started
one journey at Holland Park on the Central Line, changed at Bank to DLR
and got off at Westferry, did another journey between DLR stations
later on and went back from Canary Wharf on the Jubilee Line.

I swept my card over the reader anytime I entered or exited a DLR
station, but as I understand that was not mandatory? Unless,
eventually, you had touched in at a tube station earlier?