If you want the scanner to be sure to identify triplets you may need to tell them. In the uplands of the north of England, they basically look to distinguish between geld (empty), one and multiple. If they happen to see more than two they will call it, but unless you ask them to specifically, they don’t take the time to seek additional lambs once they’ve found two.
It may well be different in the south, but in the northern uplands, you need to be feeding twins and above, end of, so the job of the scanner is to filter out the empties and the singles. They’ll be doing several flocks of 500+ each day, too, so it’s about speed too.