My Bear Super Grizzly was marked "40X" on the riser. The dealer told me it was a 45 pounder. Always took him at his word, but I began collecting used bows with Xs that seemed to code 2 pounds. Thirty years later, I replaced the strike plate, and see the handwritten "45."
I think the X suffix means "more" and the X prefix means less. It could be 40.9 pounds or 37.8 pounds, doubt if it ever was any exact number.