I think it's the baseline fare that exists when the paring is built. Then the established fare is the amount credited when the paring is assigned/awarded. If you deviate prior to the start of the bid month then you get the higher of the two.
HOWEVER, neither of those amounts are the "actual" fare. So even when they give an established fare (which in theory should be more correct since it is a more recent look at the current fares), the amount has no real correlation to the actual fare that corporate travel books. We never get that amount.