Taste , smell , visual test .
Sauces do degrade with time. Light and heat with affect them most. However, as long as they are completely sealed, they should be "safe" to eat. Taste test should be the best determinate of the sauce quality. If it tastes funny, you can stop eating it!
Sauce packets stay good for a very long time they are packaged to be out of refrigeration for at least 2 yrs. If they are kept in the fridge they last for about 5 yrs. The only time you really have to worry about them going bad is if they are in a hot area such as your car.
When in doubt throw it out. Not worth being sick.
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