Much is said about the AAFCO. They have no legal powers. But the are the front line in pet and animal feed production, more than the FDA and the NRC. Did you know that you are not required to get FDA pre-approval before making and presenting a pet food or pet treat? That's from the FDA's own website faq.
Anyway, the AAFCO has updated since 1982 or 1981 or whatever year is being chosen.
The info on that comes from the FDA.
http://www.fda.gov/cvm/AFSS3rdDraftFramework.html
Here are some quotes from that page.
"The AAFCO OP, which is updated annually, has a section devoted to the definition of feed ingredients/additives. While FDA relies heavily on this publication, the OP is a non-Federal document, and does not have the force and effect of law."
"Gap F4. It has been several decades since FDA labeling regulations for animal feed, including pet food, have been updated. On the other hand, the AAFCO model pet food regulations have been amended nearly each year since they were adopted by the AAFCO membership in 1967. Because the AAFCO regulations aimed to keep pace with industry desires and public interests, they became the de facto accepted standard, even though they have not been adopted by every state. The public, pet food industry, government agencies and AAFCO agree that current federal pet food labeling can be improved to provide more meaningful information to pet owners about the nutrition and safe use of the food they purchase for their pets."
Be that as it may, the AAFCO explicitly states that they can't tell someone how to make a food, and the FDA requires only that the ingredients not be misrepresented, adulterated, or knowingly diseased or contaminated.
Of course, no system is perfect. But at least we have a system to work with.
As always, buyers beware.