It's not important if a date expires after freezing lamb because all foods stay safe while properly frozen. All lamb found in retail stores is either USDA-inspected for wholesomeness or inspected by state systems which have standards equal to the federal government. Each animal and its internal organs are inspected for signs of disease. Although inspection is mandatory, its grading for quality is voluntary, and a plant pays to have its lamb graded. USDA Lamb Quality Grades are based upon palatability, indicating characteristics of the lean and carcass conformation.
Conformation has no direct influence upon the eating quality.
For lamb and yearling mutton the quality grades are Prime, Choice, Good and Utility. Packaged whole cuts of fresh lamb may be refrigerated in their original wrapping in the coldest part of the refrigerator up to four or five days after purchase. Store uncooked lamb items together, separate from cooked foods. Make sure the raw juices do not drip onto other foods. Keep lamb refrigerated until you are ready to cook it.