RE: Big time scare at the shop the other night
Nock replacement due to age is always a good idea.
Shooting groups, however, can be a major factor in damaging nocks. It's fun to see that nice tight bunch of arrows in a target; but, any slight touch of a tip against a nock will not hurt the tip. The nock is plastic and plastics will age and get more brittle. Touch them with a tip at high speed and you've got a recipe for trouble.
Actually, the same facts apply to arrow shafts as well. Be careful, be safe, and good shooting.