Just to expand a bit on Garrick's answer. When we were initially discussing Efficiency as a metric there was a lot of debate between using the first throw only or the first and second throws. Technically, there is nothing saying you could do Efficiency ratings for the 3rd, 4th, 5th or even 6th baton frankly. However, Efficiency on 6th baton becomes a very different metric about how often you leave an advantage line versus the original intent which is how quickly does a team go on offense.
I think there are uses for both First Baton Efficiency (EFF1) and Second Baton Efficiency (EFF2) and I would encourage people to use both as they wish. The printed scoresheets only show the shorthand for EFF1, but that is just due to space. Any automated analysis of games I would suggest should calculate and show EFF1 and EFF2.