Maybe he was talking GL-1, -2, -3API GL-4 is a current specification and has not "been obsolete for many years." Where are you getting that information? That whole part about not being able to be tested is also not correct.
Yes can and is tested GL-4 and GL-5
Not directly mentioned: Some companies claim GL-4 for their sub 10 cSt@100°C MT type oils, and maybe that is low risk without testing.