Knots and other defects are not deducted from the price, but, the board is graded according to how clear it is. This varies with the species to some extent. I am assuming you purchased more than one board since a board 7'11" x 1" thick board would have to be 39.41+" wide to equal 26 bf. Rounding up is not uncommon but the folks I buy from are usually spot on with the bd. ft. calculation. I am not an expert on how to grade Poplar but if it's FAS or better it should be pretty clear of defects.