FE,
A tire company service bulletin has nothing to do with tire regulations. Those TSB's are put out so tech's and end users don't put some asinine sized tire on a vehicle.
I think you are being a little disingenuous with these links you are providing. The 6k axle falls into a weird slot. 16" LR D tires would work, but would lead to customer complaints and worries. So they provide LR E. This means they can use the same tire for 6k and 7k axles and keep some customers from complaining. Because of the labeling laws they have to put the LR E tire on the placard. This still does not mean, that is what must be used (what you used to say). The regulations allow for an LT LR E tire to be used on an 6K axle. In fact if one was brave enough they could use an ST LR D.