Actually, with the raw diet, they use the basis that dogs are primarily carnivorous animals who will eat mostly any meat, whether it's past the expiration date or not. Thus, many feeders feed slightly "gamy-smelling" meat. It's not recommended, but a slab of chicken a day or two past its expiration date won't necessarily hurt the dog if it has already transitioned to the raw diet.

P.S. Not every single raw diet is called BARF!!! Billinghurst has popularized the BARF diet, but many people feed via Schultz, Pitcairn, and Lonsdale, too.