I will say that I was a decorator at Publix as well. There is a standard that all of the bakeries are supposed to follow. An icing base is trucked in three times a week. The base consists of milk, powdered sugar, vanillia etc., along with presertatives. They do not tell the regular store employees the exact measurments as it is an industry secret. The mixers add butter and shortening to the base along with water in the back larger mixers. They give the decorators these in large batches. they are good for up to a week at room temperature, but most medium volume bakeries go through them in two days. The decorators re-mix the frosting in smaller batches to areate the buttercream. They add the previously mixed icing to simple syrup. They are supposed to mix on (Scale of 1-3, 3 is the fastest speed) for level 2 for at least 12 min, immediately followed by a 2min mix on level 1 to smooth out the texture.
I know this isnt the recipie but I hope it helps.
Also, all of their cakes, including the slices can sit in the freezer for 10 days before it has to be sold. So many of the cake slices, cupcakes and cakes, even the decadent ones could be 10 days old when you purchase them.
As for the icing they sell. It can be on the shelves for up to a week as well. Never buy it from the cases. Ask for a new batch. They can also flavor it for you! Anything from peanutbutter, chocolate, raspberry, almond, strawberry. All you have to do is ask and they are supposed to do their best to accomodate you right away!
No worries. I worked there for 3 years AS A CAKE DECORATOR. It wouldnt have helped for the recipe. Basically the "main secret" ingredients come in the big white block that goes in the industrial sized mixer. You add a few sticks of butter, maybe some simple syrup or just water... and mix. LOL if I could have stolen the recipe TRUST ME i would have