I always thought Johnson's split was 42.94, also, not 42.91.
I didn't realize Wariner had split 42.93.
So does Wariner have the fastest split ever?
The WC splits for the 3rd and 4th legs are very legitimate since they are measured by electronic timing as the runner with the baton crosses the line.
The split is not where the exchange is made. The split is not really where the baton crosses the line.
The split is here the torso of the person carrying the baton crosses the line.
I don't know if they can get an official split of the first two legs since the exchange is made on a stagger and they would need a camera directed at the appropriate line for each and every lane.