The measurement for improvement spans everything from very minor smoothness / comfort gains thru each accident avoided / minimized, just as with a human learning to drive.If you watch wholemars video closely, his car isn't magical or he picks demo routes purposely to show its good side. The guy just never intervene unless he finds the car stuck or about to hit something. It makes mistakes compared to human driving all the time and do miss turns. He just let it reroute and the car usually recovers. So people claiming that the car require less and less safety related disengagement is just saying it no longer want to smash into things like how unprotected turns on early v10 was really a crap shoot.
You are looking for perfect lane selection and using that as your measurement for improvements. That's just one thing out of a bunch of things....
That said, perhaps in my desire to not fill the Internet with negativeness r.e. FSDb, I am actually minimizing what happens too much. Strictly speaking of safety of lane changes, in last night's drive there were at least 5 times that I can clearly remember where the lane change (or attempted lane change) was at a spot it would be illegal. Given that it was night here and traffic was very light / nonexistent on some roads, I gave the car more leeway than I would have otherwise. In one instance it dove *across* a separator / bike lane that is inserted between the turn lane and the forward lane; in another, almost very-unfortunate instance, it attempted to change lanes into an *occupied* lane before I took control (adjacent turn lane fans out to be extra wide to ease the traffic onto the next road, so the last 10' or so of the adjacent lane looks far wider than a normal lane and so perhaps it thought it had room despite showing the other cars properly rendered on the screen). Based on prior experiences at these same intersections, if I do not intercede, it does slam on the brakes in time to avoid actual collisions, but I have learned to intercede before that is necessary. 4 of the 5 were reported to Tesla with voice notes...the first one I did let it finish the maneuver to see what it would do, then looped back so I could repeat it, disengaged at the reasonably-should-disengage-point, and provided the voice note.