I'd like to see where this is written, because I try to stay half way up to date on the applicable laws and I have not see this one.  As I'm sure you know there seem to be plenty of people with crazy ideas that they come on here and claim are law.  I'm certainly not putting you in that category, which is why I am interested in what you find out.

As far as my own standards, I won't accept a tire from the supplier which has a casing over one year old.  I realize that's pretty tough, but we do not put miles on fast enough to be buying old tires...we might get to 10 years old before we wear out a tire without it being old when installed.   I don't throw tires away for casing date, but I will pull them off of the road truck or trailer and move them to the local ones.