I think GF were created well after A, B and CSo, there is already more safety built in in ZH-L16 C. Maybe the use of a lower GF low dates from ZH-L 16 A?
And in the article from prof. Doolette I read: “Tyler Coen at Shearwater Research Inc. noted that GF settings recommended by Fraedrich modify ZH-L16 M-values so that approximately the same level supersaturation is allowed at all stop depths.”.’
Another argument for parity?
Eric Baker mentions them in this document btw
Gradient factors explanation from E Baker, he references the previous paper so must be written afterwards.