if the engine with a closed loop control system can run at lambda = 1 and leaner, there's no reason why the same engine without the closed loop lambda system can't as well. what has changed?

as i understand it, you need a base map for if the lambda sensor stops working, but a closed loop system will tweak the fuelling to stay around the lambda = 1 point without using the values in the base map. i see no reason why the base map can't / shouldn't be made to be as close to lambda = 1 at those speed and load points where it is suitable to do so.

i could be wrong, and am just a diy person like yourself that is hoping to learn all of this.