In that case, your dad shoulders the responsibility for that, and lack there must be a lack of concern for the animals that he is slaughtering if he KNOWS he doesn't get a clean kill. That's aweful if he knew this and did it anyway. That's on your dad 100%
It was a different time and it is doubtful you would have complained back then. Give Birdinhand full credit for learning from it and moving on to more humane practices.