I think there is a fair chance the JWs are right that the substitution of YHWH/IAO with kurios was a Christian innovation dating to the second century CE.
I am reading it differently. I think Hurtado, as well as the source he mentions by Martin Rösel, is saying that the LXX 'autographs' if you will, contained kurios, but the substitution of the Hebrew-letter tetragrammaton was done later by copyists. Maybe I'm just not getting it