>>the grade determines how perky the egg is, as well as how old the egg is.
sorry luvs - some misinterpretation there.
USDA grading does indeed address the internals of the egg as can be observed via candling / inspection / etc. and quite bluntly about all that shows up is the size of the air sack - the "condition" slash more specifically the viscosity of the yolk or white cannot be evaluated by those methods.
has nothing to do with "absolute" age. it is entirely legal for an egg supplier to have market stock returned that has gone past the 45 day package date, re-wash, "re-process" - put on another "new" date another 45 days out, and re-sell the eggs per the USDA grading stds.
and, don't forget, all those kinds of companies are all the most upstanding / would never fudge / lie / stretch the truth / ignore the grading stds / break the law kinds of places. right..... so now that we know all the crooks are honest,,,, moving right along.....
it is entirely possible - and "legal" - that one or more (egg processors "co-mingle" the returned stock . . . ) of the eggs in the carton "freshly dated" is/are 60 - 90 - 120 - 160 days "old"
there is _NO_ tracking mechanism to this approach.
here's a fairly "readable" version of "egg grading" -
http://usda.gov/wps/portal/usda/usd...EARCH&Go_button.x=21&Go_button.y=11&site=usda
the details past that get real thick real fast , , ,