sic 'em reds said:
I understand the same way as WR. If your herd is tested clean, you don't need to test every year. As long as any animals brought into the herd are BVD PI free.
Maybe what the vet school is saying, by testing all the calves each year, if you happen to get a positive in those calves, you can remove it from the herd so that it doesn't spread the virus to the other cattle/developing fetuses??? Or maybe just leave the calf in the herd and vaccinate the others for free

...not really.
If all dams previously tested negative, I think you could assume the infected calf's dam became infected during pregnancy, and you could maybe step up your vaccination program to help prevent it from happening again :? ??? I know of some herds vaccinating both prior to breeding and again in the fall.
As for getting paid a premium at shipping time, I asked my buyer about testing my calves, and he said he wouldn't worry about it since over several years of posting cattle, they haven't found BVD to be a significant problem. I'm sure there are feeders who would disagree. I think testing benefits the cow/calf producer more.