Agree with your math and other details. I add: Also remember the dialog about 7 billion people from Coop's father in law. I guess I felt like now there is only 1 billion (but that's a wild ass guess)? (As they said that India shut down same as theirs, so it isn't "wiped out gone, but maybe China is?")
was clearly a long world war as the result of food shortages
I'm not sure the war was about food shortages in it's cause. I felt that was symbolic of ignoring the worm hole, and ignoring climate change - that caused the food shortages in the first place. I think the root of the cause of WW3 was more the failure of the Eye of Reason and the Socratic Mental States of the United States of America and it's attitude of Global Conquest - not Democracy. As we have had for far too long already. This failed Eye of Reason is symbolized by Coop/Murph in several ways. 1) Apollo denial, 2) The elimination of Founding Father Public Libraries, 3) failed Health Care System due to greed logic (not Eye of Reason and Individuals) in Coop's MRI rant; and the lung cancer that Murph confronts with her brother, 4) Murph and Coop not being invited and having to cut NASA chains, 5) Mann's Socratic Logic as "the Best of Us". 6) Favoring of Propaganda (Edward Bernays) over Reason by the Professors.
All these are USA problems since World War 1, and notably since Easter Sunday 1929.
We fucked up, we had a war around 2040(?) - and we had built robots say in 2030 for military focus. We also knew of the wormhole far earlier - and I guess the leaders decided to ignore that intelligence in favor of conquest games on Earth. We did not use the American Eye of Reason during peace time to turn around Global Climate Change, nor did we follow the USA $1 Bill Eagle, who is to look at the Olive Branch (his eyes point to one claw). That's really the world we live in now, one of perpetual wars and not Ideals of our Founding Fathers. The USA $1 Bill has an Eye of Reason. Much of this is explained in the 1986 book The Inner Reaches of Outer Space. That Book also has a story about a Worm Hole Journey of Corn Pollen (climbing a Corn Stalk) that passes with one Male and one Female cheered by the Nation.
P.S. I wish to point out, as Inner Reaches of Outer Space explains, it does not matter what the two brother authors say in interviews. This film is a "Public Dream" and it can have meaning beyond the author's own self-awareness.