The way that I understand it is that Disney does not keep track of it in the "big system" so to speak. In other words, the only way that Disney does regulate it is at the cash register.
For instance, if you are a family of two adults and two children, then at the cash register (during one transaction), you could purchase no more than two adult meals at one time and two children's meals at one time, if the restaurant has a children's menu.
However, if you were at a place that offered no children's menu, then that place would not keep you from ordering four "adult" meals, because they wouldn't really be "adult" meals at those places. They would just be meals. Period.
But if you are at a place that does offer a children's menu, then they will limit you to two adult meals during one transaction. But even at those places, if you and your spouse both ordered an adult meal and then a few minutes later your spouse was still hungry, he or she could go back to the same register and order another adult meal. Disney does not regulate how many credits you spend on a given day. (They only keep you from purchasing three adult meals during one transaction, if your party only has two adults.)
Also, once your credits are gone, they are gone. Even if you theoretically spend them all on the first day. Hope this makes sense. It is confusing to me, too, and I may be mistaken. But this is the way that it has been explained to me, and it seems to be the way that it works when I am there. Someone please correct me, if I am wrong!
