If Purina's customer service is like everyone else's, they recieved a generic apologetic sounding response with a vague mention of feed formulations, and a coupon to buy more.
Every Feed Maker is contantly adjusting their recipes to hit a desired nutritional target - its not like baking a cake, where you add X eggs, x flour, x leavener, x sugar, x flavor and bake for set time and temp.
When the corn comes in a little low in protein, something gets increased to compensate. If the soy meal is higher ptotein than normal, or the field peas, maybe they cut a bit out. Then you have regional mills altering composition (still looking at the end goal, a specified nutritonal label) based on local pricing. and since cracked corn isn't cracked corn, or at least, not identical cracked corn - depending on the field harvested, the rain/dry weather pattern etc, just as other ingredients vary with first cut, second cut... etc you should expect your feed to look different all the time.
Which is quite different from feed companies flat out reformulating different mixes to alter the guaranteed nutritional output - which appears on the tag, but likely nowhere else. I have seen evidence that a number of manufacturers (if not most of the majors) have altered the targets over the last few years, due to reduced availability and increased pricing of certain key ingredients, in order to protect a price point. That is, the "Flock Raiser" you bought this year may be milled to a different target nutrition than the "Flock Raiser" you bought three years ago. Methionine is one of the first things that looks like it wass cut, Lysine the second - leaving the total crude protein number (the thing most people who get past "layer" "grower" and "starter" stop at) - while the actual nutritional values have declined. We may also be seeing increased willingness to use things like oats, barley, higher tannin content peas, etc whose antinutritional factors are harder to characterize and are nowhere displayed on the label, reducing the ability to make use of the rest of the content by some tiny amount.
These are all the sorts of changes that would escape the notice of most, and likely be attributed to other sources - the new hatchling chicks being just a tiny bit smaller on average, a week later to start laying, the Cx not hitting desired weight as quickly. They are also things which likely would have no noticeable change in adult birds, physically.
That's my impression, anyways, still gathering data points.
The 1st 2 digits refer to the year, the next 3 are the day. (So it’s Jan 3, 2023). The SGF is the mill, in this case Springfield.
This one, the year is ’22, and the date is 276th day of year or Oct 4. The STJ shows it was milled in St. Joe. 
