What shelf-life information is included on packaged (pre-cut) lettuce?

Packaged lettuce usually carries a "sell by" or "use by" date determined by the processor. If dates are specified on packaging, they refer to quality rather than safety. Nevertheless, it is wise to consume packaged lettuce by its "use by" date, particularly if packaging has been opened prior to the date. This is because anti-oxidative gases that preserve packaged lettuce escape from the original packaging once it is opened.
 
Source(s):
GourmetSleuth.com "Food Storage Guidelines - expiration dates"
GourmetSleuth.com "Food Storage Guidelines - food storage"