On directv at least I've already seen two overflow channels. Yeah CSN has 2 overflow channels that I know of. The Cubs were on one earlier this year. Not sure about 3, but I'm sure they could find an emergency backup option on the chance that the Cubs, White Sox, Bulls and Blackhawks are all playing on the same day at the same time, on the same channel (don't forget the Hawks, Bulls and White Sox are still on WGN and the Bulls, Cubs and White Sox all occasionally play on the U). It would probably happen 1-2 times a year tops.