I came up with the naming scheme here. We picked n for Intel as I could be confused with i3/i5/i7.

Early work was done in AMD and we had an a1 series pre launch.

IIRC, g is for Google or Generic where there are no promises on architecture. And f was for fractional.

I've been out of Google for 2+ years now so reality may have drifted from that original scheme.