I personally dont pluck anything under 15, and when i do i replant them so they can naturally replenish what i have taken. I mean its different buyers, ends up with different results . some simply buy by the pound, some buy it sectionally like... 3.5lb for 1350 6lb for 750 ect.
So if you dig one under 15 you put it right back in the ground to replace the ones you did keep? I have never heard of someone buying "sectionally" everyone I have been to or talked to buy it by the pound. If you bring in 3.5 pounds you get paid for 3.5 pounds.