What shelf-life information is given on a mayonnaise jar?

Generally, mayonnaise jars say, “Best if/when used by ______ .” Most jars on store shelves are dated 4–9 months in the future.  The “best by” wording implies that the product can be used after that date. “Refrigerate after opening” is on every mayonnaise jar.  (The unopened jar doesn’t need refrigeration but should be stored in a cool, dry place.) Preservatives are identified by name and followed by an explanation of their purpose, such as  “to retard spoilage” or “as a preservative.” Note: the jar doesn’t tell you this, but once it’s opened,  the “best if used by date” no longer applies.
 
Source(s):
Labels on mayonnaise jars