Some of those numbers dont make sense to me.
Bat speed 71.8 Exit speed 67
63.4 70
84 73
65.8 73
How can an 84 mph bat speed end up with the same exit speed as a 65.8 mph bat speed?
I believe some of the difference or variances comes from different bat manufacturers. Some bats are simply better than others.
Also, some of the difference comes from different bat weights. For instance a girl may have a slower bat speed if she swings a 34-8 than a girl that swings a 33-10. To put it simply exit velocity with the same bat should be higher with the heavier bat if the bat speed is the same. Of course a lot of the exit velocity has to do with barreling the ball up on the sweet spot.
Personally I don't put much emphasis on bat speed in these types of data bases. Exit velocity is the important number.