You're completely backwards. If only the string creeps (not stretch) the drawlength gets longer and the weight goes up. Probably what's happened is that both the string and cable have crept over time decreasing the prestress on the limbs, thus the weight goes down, even though the drawlength may have stayed essentially the same.

Just how much is the weight down? Most bows go a couple pounds over the rated weight, but most companies note that weights can vary as much as 3# on the downside, too. In reality, ask yourself. Do you think a deer knows the difference between 70# and 67#, or 60# and 57#. A passthrough is a passthrough.