What does the date on a carton or bottle of lactose-free milk really mean?

Depending on the applicable local laws, consumers will see a “sell by” or “use by” label or possibly both.  Consumers everywhere should assume that this date applies to the refrigerated, unopened product. The date relates to the milk’s quality, NOT its safety. It tells you how long your milk is guaranteed to remain fresh before it develops the food-spoilage bacteria that cause the milk to taste sour, smell bad, and/or lose nutritional value. Pasteurization and other sanitary milk processing methods kill the dangerous pathogenic bacteria that can cause illnesses, said Cary Frye, vice-president of regulatory affairs for the International Dairy Foods Association, which represents the U.S. dairy manufacturing industry.
 
Source(s):
U.S. Department of Health and Human Services and FDA Center for Food Safety & Applied Nutrition: “Grade ‘A’ Pasteurized Milk” Ordinance
Cary Frye, vice-president of regulatory affairs for the International Dairy Foods Association