Plot hole: When Veronica tells Mac that she was switched at birth with a girl who was born the day after her in the same hospital, Mac repeats that the girl's birthday is the day after hers, as if she already knows what she's about to read on the paper that Veronica gives her, which is that she was switched at birth with Madison. That would make sense, because Madison was making a big deal about her birthday earlier, and it's reasonable that everybody would know when it is. However, if Mac and Madison were sent home with each other's parents, then they were also assigned each other's birthdays, meaning that even though Madison was really born the day after Mac, Madison would celebrate her birthday the day before Mac celebrates hers.