I make arrows for my friends and family. Only one of them wants aluminum arrows, all the rest want wood, so I keep a variety of spines on hand. When someone wants arrows for a particular bow and head weight I make a couple, we shoot them. Besides playing around a little with brace heights on recurves now and then, the one that flies right wins. People's draw lengths can grow if they are new shooters. Likewise people's draw lengths can be shorter in real use than the draw lengths that they measured, even though their form is on the whole fine. In those cases, changes in point weights have been enough to fix the problem. I give new shooter that do not have their form settled in and extra for their first set. More often than not when someone with less experience says the arrows shoot one way or the other, it is them and not the arrow if the spine is anywhere near close.