Why does Air Techniques Chemistry have a “Best if Used by” date and not a specific “Expiration” date?

Chemistry solutions age and gradually lose their chemical energy over time. Their service life does not end with an abrupt event, as when a light bulb burns out.  Consequently, the day after the “Best Use” date, there may not be any perceptible change.  The ‘Best Use” date is imprinted so users will be aware that Chemistry activity level is or is not within the manufacturer’s performance specifications.