I'm sure there is an after the calculation QC function considering all the tribulations with BV2.
It was called manual checking. BV2 most often is calculated in the following way:
1- Unit is made using MML. BV is recorded
2- Unit is entered into one of our many spreadsheet programs (we have several for different kinds of units)
3- If 1 and 2 agree, we stamp it "gold"
4- If they don't agree, we run it manually and look at both MML and the sheets for errors
5- We random sample completed lists of units with hand checking to see if we still screwed up.
That's for most units. Some units require more intensive work.