You could stick a thermometer into the bale. I would say if you think it is tough it probably is. Almost noway so far anyone could have dry baled good alfalfa yet around here. Alfalfa will feel moist to the touch anyways and if it is marginal moisture it should be heating up right away to a normal 120 degrees. If it gets above 120 then I would be concerned about how well it is curing. It could take a couple weeks for it to become dusty from mold spores.