I've searched around on the internet, and I haven't found anything saying Shell has reformulated Rotella T4. If anyone has this info, please post away. From what I've read, most of the Major companies make slight changes to their formulas from time to time.
I don't use Rotella in my Semi Truck, but Rotella T4 is used by most of the Owner Operators that I've talked to. I was told by a FedEx Freight driver that their shops use Rotella T4. That one account alone has to be a very lucrative account for Shell, and I'm sure FedEx regularly runs UOAs on their fleet.
My guess is if Shell has reformulated Rotella T4, it's been done to improve it in some way. It carries every major engine manufacturer's approval for Commercial diesel engines. IMO if the new formula meets your engine's approval, use it with confidence.