Just a quick one that came up the other day. We went from almost no Fattys to all of them in one turn. We then drew the Fatty sewer card. Am I right in thinking this would cause an activation for each manhole cover we couldn't spawn Fattys on? I assumed yes as it says "Sewers located on a tile with at least one survivor will spawn..." implying multiple spawns are taking place.
It's surprising how often this happen. One turn there's no fatties then they all come out to play. We had a mission with all 8 of them in the same zones (but 2 chainsaws, which kinda made it fun!)