I think if Bolt really pushed himself, he could have broken sub 9.5 seconds at the peak of his ability. In all races where he dominated, we see him slack off right near the end once he realizes how much further ahead he is of everyone else.
Personally would argue these guys do this same sprint/distance so many times in practice/competition that they generally implicitly know when they're running a WR type time and generally don't slack off (in this video he's not in any threat of being caught but still presses on for the WR).