On an unrelated-yet-similar topic is Amsoil and DEXOS compatibility.
https://blog.amsoil.com/gm-dexos-and-lspi/
AMSOIL synthetic motor oils meet or exceed the latest industry standards, including ILSAC GF-6, API SP and GM dexos1 Gen 2.
You can safely use our synthetic motor oils in engines that call for those specifications.
In fact, AMSOIL achieved 100 percent protection against LSPI in the engine test required by GM’s dexos1 Gen 2 specification.*
So they meet the spec, but just don't have the stamp/certification?