Whether the stop margin was 800+ feet or zero, they still did not depart with less runway than their performance calculations allowed. Even with a zero stop margin, the aircraft was still calculated to be able to lose the engine at V1 (or later) and continue the takeoff. They did not takeoff with insufficient runway.
Not true! Intersection B1 gave them about 9100'. TOLD was figured for 9800 feet. Definately a contributing factor.