RE: shooting the spine out of an arrow?
Doesn't seem to be an exact answer, MilDot. Even in the same dozen, some arrows hang onto their stiffness for quite a while whileothers go bad after only a couple of dozen shots. I think it's a good idea to get at least one new dozen every year. I'd say definitely right before hunting seasonto make sure the arrows are as good as they can be,or any time you notice your accuracy and consistency isn't what it should be.Especially if tuning the bow doesn't help.
I think it's very likely that a lot of the tuning problems that are posted here couldeasily be traced down to worn out arrows.