A grade assigned to a player is subjective and arbitrary.
I would ask, "whose BPA?" Iow, where does this grade come from?
To be a true BPA, it would have to be a consensus from among all the accepted graders to arrive at a final grade number and I don't think that happens.
One only has to look at all the different big boards to see how widely varied they are after the middle of the first round and even then, there are slight differences among the top half.
Then like you say, each individual team may have their own grade designations.
This is why we see "reaches" every year.
That is why I attempted an
aggregate draft position for the top 100 a month or so ago.