Why is anyone entertaining this "story" at all? A childless couple would have wanted one of the baby siblings, not an older child who knew who she was. But JMO.
Because it's far away from being a contradiction in itself at all!
Nobody said, that - if this story turns out to be true - Maddie has been the main target at all!
Let's just assume, this "kidnap by order" - story to be true. One of the twins, probably Amelie, might have been the main target, because you are right, it wouldn't make a lot sense for a german couple to order a native english speaking girl, that has almost been 4 years of age at the time. Of course, it speaks a lot for the assumption, the couple would place an "order" for a way more younger child.
That doesn't change the fact, that an alleged kidnapper would have been checked out the apartment and all of it's movements days before he would snatch any kind of child. He would have known who lives in the apartment and what usually happens after the three kids went to bed. Just like what happened all the time in the days before may the 3rd.
Just imagine the "original order" to be cancelled, shortly before the planned strike. Probably in a half hour call on may the 3rd?
How would the alleged kidnapper, who might be a vile paedo as well, react? Going home without the chance of making money out of the human trafficking, or considering the kidnapping of another small fair haired but slightly older girl, probably for selling it otherwise, or his own pleasure and probably the chance to make some money out of it, by selling some "other stuff" on the dark web?
That's the main question imho!
So many people, police forces, profilers etc. have been quoted that the disappearence of Maddie just could have been taken place by someone who tried to steal from the apartment and made the decision to take Maddie by chance. Nothing valuable seems to be missing from 5A, except a poor little child. So we just don't know if the original plan was to take one of the twins maybe and snatching Maddie was just a kind of substitute at all?!