This reminds me of Fred Bear's philosophy about draw weight. Anytime Fred felt he needed a little extra zip, he just drew the arrow back a tad bit more.
This is why it is probably a good idea to measure draw weight by actually drawing the bow and feeling the strain. My first real bow was a 73 Super Grizzly marked "40X" on the riser. Years later I replaced the leather strike plate and saw the hidden "45" measured weight. If I really pull back, I can get about 48 pounds from my 40X. The only accuracy that really matters is where the arrow hits.