About 14 years ago I was at the shop and shot the back end of one arrow with another arrow. It blew up the nock and put about a 3/16" half moon indentation in the back end of the arrow. Never saw any cracks or anything other than the smooth indentation. I walked into the work room, cut 1/4" off the nock end, put on a new nock, and shot it. Then I marked it with an S for "short" and took it home. Put a BH on that arrow that season and shot my bull with it. Brought it home, cleaned it up, and shot another bull the next year with that arrow on a quartering away shot. That bull fell on it and snapped the whole fletched end off the arrow. Then I retired it. But these were also the toughest arrows I've ever shot and weaved. I've never seen any cracks at all on them anywhere for over 10 years.
For me, if a new nock fits tight, I'd shoot it. If not, then I'd keep trimming it down until it did and was still long enough. If it got too short, then toss it.