Tor, I like your analysis but there are some caveats. The first is the CAA, which I did not include in the Inner Basin following Wipneus' convention, but that has never reached zero volume at minimum. I'd say add about 0.2 for a total of 4.5.
The second is the Greenland Sea, which historically has never been "empty" at minimum, but came very close to that in 2017. I'd say add 0.05, with the total remaining at 4.5.
The third is that day 260 is not necessarily the minimum, so potentially the minimum could come in a bit lower.
In any case, the big wildcard is the CAB.