Only other way I could come up with is that 2 wilds make a CB then 2 CBs make F1, and that f1 could only come from CB not WC. (basically just another step, but would not make much sense). Hopefully your understanding is right.
Wild Caught is F1. Every generation away from F1 is another number added.
Two wild caught parent offspring is F2. The offspring of that generation is F3 and so one....
I have heard the way that zoodiver just explained, but I have also read that 2 unrelated WC are F0 and their progeny is F1 then two unrelated CB from these F1 of these same progeny line are F2 and so on. Don't know which is accurate.
This is what I found googling: The first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types
F1 means first filial generation. So with the above definition, a F9 x F5 of two different bloodline makes F1
Thats why all the rave about these "tags" are pretty much pointless...and for all we know (unless you caught it yourself) we have F4 that some sold as F1. So we go around selling them as F1 to the whole world. And also even WC could be from brother and sister is the waterhole is small enough, also as odds in life and nature goes it could happen, and sells as WC parents WooooHoooooo Yay Lotsa money for inbred WC.