DS is nearly 4 months and the majority or his bottles still have number 1 teats a couple have number 2 teats on them, I notice no difference in the way he takes the bottles depending on the teats and usually takes his milk fine (drinks the majority at night) and usually doesn't take him long to take a full 6oz if he's in the mood. Should I be changing all the teats now or leave them as they are as he is taking the milk fine?