The words "up to" and "at least" have their usual meanings. And always beneficial to developers. eg "up to 40% affordable" = 19%, "at least 1500 homes" = 1850 homes.
While "affordable" and even "social rent" don't translate into what we thought of as "Council Houses and Flats" back in the 50s and 60s.
It's Orwellian, I tell'ee.