That's never been confirmed. It's not really known why Sunbow decided to call Jetfire "Skyfire" in the G1 cartoon. Changing the character design alone was enough to evade legal issues with Harmony Gold -- they don't own the rights to the Jetfire name, only to the VF-1S Valkyrie design.
re: "Why Skyfire?"
Because Classics Jetfire is not a Valkyrie VF-1S. HasTak very carefully (and cleverly) designed it as an hybrid between a VF-1S and the G1 cartoon/comic design of Jetfire/Skyfire. It bears a vague resemblance to those designs, but doesn't actually look like either one.
I believe that was Jetfire_in_the_sky's point.Masterpiece is all about engineering G1 Transformers to look more like the cartoon, so an MP Skyfire (Jetfire was only ever called "Skyfire" in Japan) would definitely be based on the cartoon model, and not at all about emulating the toy.