Quite right L377, all fuel is available for use.
The only difference is the non-normal configuration of the pumps and cross feeds if any of the main tanks has less then 1T of fuel remaining.
I understand that the crew had doubts about whether the fuel in the main tank associated with the shutdown engine was usable or not. Since then, I believe all crew have received a briefing on how to use this fuel to run the live engines via cross-feeds earlier in the flight so that the tanks are approximately balanced on arrival. However, this is just to reduce any trim drag due to the imbalance and not any fuel feed issues.
All crew have also been shown in the simulator that the aircraft will run all 4 engines quite comfortably with a main tank empty if all main pumps are on and all cross-feeds open. This of course would apply on 3 engines as well.
Boeing designed the aircraft so that any engine can receive fuel from any combinations of main tanks making all fuel usable.