I do know that the reason Killavullen amalagmated with Castletownroche at gaelic football was becoz the football side of CTR folded due to lack of interest. Both sides field seperate hurling sides. The last 2 sides they met this yr, Glanmire and Mallow, are one parish- so the all bar 2or 3 remark seems way off the mark.
btw Ballyhale Shamrocks are made up of 3 seperate parishes, didn't stop them playing in the Leinster championship.