I don't know whether you are wrong or right either, I was just relating what I did as a reference for you, as I know mine is all seemingly working fine.
I just copied the 3 MAC addresses (and the Secret) from the original CFE of each of the TM-AC1900's I was converting (once I back-revved firmware and got SSH access) to a copy of the Goggles99 CFE, and noted (as others have) that the first 2 addresses are the same and the 3rd is 4 greater/higher, but "4 greater" being in hexidecimal addition not decimal addition of course.
Goggles99 concluded that his CFE was only needed for the AiMesh Router (master) anyway to make AiMesh finally work (thanks again to him for his great find), but my thinking was to just "do them all properly" the first time, which also means in the future I don't have to keep track of which one is the "Router" as they are all completely "fixed" and any of them can be the Router (in AP mode in my case, none of them will ever be my main house router actually doing the ... routing).
StephenH
This is a mistake I made. I just copied the same MAC address in all the 3 fields. Now I have to figure out how to fix it. Are the first 2 MAC addresses the "real" MAC addresses and the third is 4 higher? How do I get the "real" MAC address - is it what shows up in GUI?