A few days ago, in How Fresh Are Your Eggs? I pointed out that eggs for sale can easily be 30 days old. The day the eggs are packed is stamped on egg cartons, but it’s impossible to know the day when the eggs were actually laid.
I sent an email to Mark R. Lemon, Federal-State Supervisor of the USDA in Olympia asking about the difference between the date eggs are laid and the date eggs are packed. This is what he emailed to me today:
Eggs of current production for USDA inspected eggs, are eggs that are no older than 21 days from day of lay. The code date on the carton represents the date the eggs were packed into the carton, but the eggs are allowed to be up to 21 days old from the day of lay. Most eggs packaged these days are from the same day of lay and maybe up to a week old. It is not very common for a plant to even push the 21 day maximum. Eggs are produced in such high volume, that eggs do not sit very long before they are packaged and sent to the stores. I hope this answers all your questions, thanks.
In other words, egg producers have up to 21 days to pack eggs. So when you see eggs that were packed 30 days ago, there is a chance, though not likely, that they could have been laid as long as 51 days ago.