Re: The bold statement. Why wouldn't it be valid to use GF-6B 0W-16 in place of the old 0W-16 SN/SN+ ? What would be so different about 0W-16 GF-6B SP formulation that wouldn't allow it to be used in an engine calling for SN or SN Plus 0W-16? They are talking about vehicle back compatibility in term of oil viscosity, not oil formulation.
As mentiioned earlier, they don't want people just seeing the "GF-6" spec and then grabbing a 0W-16 thinking it's OK for engines that call for xW-20 or higher.
That is my conjecture but some of their statements are not concise enough. From ILSACs standpoint you were never supposed to use anything other than specified grades so GF-6B is no different than previous certifications in that regard.
My guess is it's no different than cars programmed for 150C Protect Mode and 5W-50 and 120C Protect Mode and 5W-20. Reprogram the "Nanny" and fill it with 0W-16.