The Cougar Ace paper uses the term “bilge ballast tanks” the more common term is double bottom ballast tanks. The paper also uses “2 Port” (2 port + 2 starboard) meaning two different sets of tanks (four tanks total) but is confusing because 2 port would be the name of a specific tank.
The conclusion of the paper here makes it more clear.
So four separate ballast tanks with a total capacity of 4000 tons was pumped out during a ballast exchange. This reduced the GM (called MG in the paper) from something close to the required minimum (about 1.4 meters) to 0.05 meters or less.
At the time the ship had about 450 tons of fuel on board, assuming consumption was 50 tons/day is about 9 days which sounds like “minimum reachable” with a margin meaning they planned to bunker USWC.
According to the calculations even pumping out four ballast tanks the incident would not have occurred if they had a few more days fuel aboard.