Based on my experience as a Ford parts guy back in the day, engineering numbers at the end indicated updates.
I suppose they could have changed manufacturing processes to fix it, but despite all of that, they've yet to admit fault/advise customers of what the issue actually is. Dealership doesn't even know. They just replace the motors per the TSB.
100% correct. If they changed any part of the manufacturing design, the number/prefex can change also just from suppliers. I'm a Ford man, but this pisses me off.