I wouldn't take a stringster result too serious. Had also results which were 1 kg higher after I strung them. Additional it also depends how a stringer treat your request of 27lbs. I would hand out a 26x27lbs job. A different stringer can also hand out a 25x27, 26.5x27.5, 27x27, 26x28, 27x28, 27x29 and so on. And all of them would be correct based on their individual explaination for that.