You are correct with A and B, but as soon as you went out to zone 6 on a train the zone 1-6 cap is the one that applies. You didn’t reach that cap.
If your Oyster card was a plain blue adult card with no discount entitlement then the journeys would later be run through the back end and you’d get a credit. Sadly the back end only deals with adult fares so you won’t.
Hope that helps.