How do you know if you have "mixed" for your twins?

My sister had twin daughters three months ago, they came home from hospital about 3 weeks now and they are completely identical it is not something different about one of them. I know that time, things will change, but right now my sister is afraid she has "the mix, first they got into a routine to remember who was who, by their outfits, because of fatigue, she dresses them before bed, and I forgot to remember who was who, she put both in Moses and their baskets in the morning does not remember who was who. I know it sounds silly, but she does not know yet. Is it really possible to have twins growing up called each other names because they were "exchanged" over. Is it really important? I offered my help and support, but I a full house me, this happened to anyone here?

Oh gosh It's a little scary in a weird way. Interesting question! She is tired for obvious reasons, I think anyone else could do the same thing, perhaps when she is awake, she remembered. Maybe you could buy her special identity bracelets with their name on a gift to his and your way of helping. Other then that you could suggest she wrote their names on the labels of their clothes.