Rule of egg
This seems to be a pretty good rule of thumb, literally. It applies specifically to Safeway's eggs, but I'll bet it generalizes to other types using cardboard cartons.
You can spot a broken egg
somewhat reliably without actually opening the carton... or at least you can get a pretty good sense of what you're going to find when you do open the carton.
Wiggle the front part of the lid.
If the carton is firm and tightly latched, the eggs are good.
If the carton is overly flexible and loosely latched, at least one egg is broken.
I can't guess the causation. Obviously one major bump will break an egg, but one major bump doesn't soften the carton. Perhaps a carton that has been softened by too many recyclings can't protect the eggs from
minor bumps?