Thanks for the speedy answer!
OK! That's almost what I had deduced but it clarifies everything a lot. So, all skills start at d4 and get upgraded (or not) from that; there are no "unrated" skills without a die rating. Unrated is d4.
And to be clear I only talked about the pyramid to use an easy to get Fate term; it looked appropriate given the example GMC having 1x d10, 2x d8 and 3x d4! There's no confusion about it in your text, it was just my choice of word!