According to Duncan Hines, its boxed cake mixes feature a "best-if-used-by" date rather than an expiration date. Cake mixes manufactured by Duncan Hines can be used indefinitely after the "best-if-used-by" date. The company, however, does not guarantee the quality of the product beyond the "best-if-used-by" date.
Betty Crocker boxed cakes feature expiration dates and can be used past their expiration, though the company does not guarantee the best results in baking. Some issues that home cooks may encounter with the use of boxed cake mixes used past their expiration or recommended-used-by dates include a smaller rise during the baking process, resulting in a flatter cake, and less intense flavor. Betty Crocker recommends using expired cake mixes in dessert recipes that feature cake mixes but aren't specifically cake, so that any deterioration in volume or taste is not as evident. According to NPR, the National Food Lab assigns shelf life to foods based on a scale of degradation. There is no baseline number for foods, however, that determines that they are no longer good. Rather, the individual companies choose the number at which they want to warn consumers that the product may no longer be edible. This is why many foods are actually still edible past their expiration dates.