Oh yes they do. These folks know exactly how to calculate based on the FACT that the oil is entering the casing at the bottom which travels the depth of the hole and exits and that pressure can be measured at the top where the blow out has occured. That gives them a rate of flow after a few more calculations. Absolutely they know. Just like they knew they were risking a lot by a review of their behavior and events before this catastrophe.
I worked in the oilfields... I have seen/heard the disagreements around the rig floor. This is the ultimate catastrophe based on the inability to make a safe decision to do the right thing.