To me, it seems clear that the intent is for two distinct/separate critical effects.
The example given says that it's possible to give three face up damage cards in an attack, using XX9 and FCT. THAT IS THE INTENT. Clearly there is some ambiguity due to the wording of XX9 being written when only one critical was possible.
Also the rules relating to an attack, were written with only one crit in mind, so they should be modified to account for two critical effects.
So I'm going with 3 face up, until the FAQ says otherwise.
I think it's safe to assume the Intent was that the crits would stack and until faq'd that's how I would treat it
Of course it's possible they faq it the other way but I just don't see it happening