I remember reading somewhere that if firecaulk is to be used, then maximum allowable MN cables
was 2. Is this in the building codes and not in the NEC???

I know in article 334.80 AMPACITY, it states that we must refer to table 310.15 (B)(2)(a) to adjust the ampacity for more that two NM cables passing through wood framing that is to be fire- or draftstopped using thermal insulation or sealing foam.