When you are testing for potency, THCA is irrelevant. And it converts into more than just D9 THC. So when the ultimate goal is finding out d9 thc, why even use a test that calculates THCA? Maybe because that method produces higher numbers due to the process. Only people ingesting raw THCA, are people juicing cannabis, anyone else is using a form that THCA has already been converted into D9, D8, CBD, CBN, CBG, etc..