Date guide
Use-by and best-before dates mean different things.
A use-by date is a safety date: do not use the food after it, and follow the storage instructions that make that date applicable. A best-before date is a quality date, and it is not the same instruction as a use-by date.
Use-by: a safety date
Do not use appearance or smell to judge food after its use-by date. Follow the storage instructions that make that date applicable.
Best-before: a quality date
A best-before date concerns the quality of a food. It should not be treated as the same instruction as a use-by date.
Opening adds another instruction to check
Some supplier packs specify how soon the food should be used after opening. Print an ingredient label and set the shelf-life days from those instructions. The label does not replace the original date.
Use the right date rule in your software
Set the rule for the actual food and stage, then check how it appears in the label preview. Changing or reprinting a label does not change the age of the food. InstaLabel does not decide a safe shelf life.