In spite of the fact that increasing numbers of food processing companies are moving to open dating it is not yet universal. For those products that do not come with a plain 'best used by' date it is still possible, albeit with much more difficulty, to determine the rotation period for that specific product. For a processor to move their product in interstate commerce it must exhibit a packing code. This allows them to easily track their product for purposes of stock rotation and in the event of a recall. These packing codes are usually a series of letters and numbers that indicate dates, times, and sometimes places of manufacture.
These dates are not 'use by' dates, but the time the container was actually filled. As they are not really intended for general public knowledge these codes are frequently unique to a particular processor and are not commonly published by them. It is possible to get the keys to these codes by contacting the processor and asking how to decipher the dating code for specific product lines. Over time, readers have been doing this and the code keys below are the ones that have been sent to me.