I'll put in my two cents as it's just my interpretation and I'll probably be corrected here shortly.
I feel 7.9 is a way for manufactures to stay honest to table 7.1 and 7.3. They have to make sure that the product is meeting the minimum standard.
In a shop environment, I shoot studs per 7.6.6 to create a WPS and welder PQR if needed. After that as far as production I resort to 7.7 which does have stipulations as far as start of shift requirements.
That is just my understanding and interpretation, I may have been doing a lot of extra work this whole time, but I've always been comfortable with it. Testing two studs at the start of shift usually doesn't take that long.