She is the most famous missing child in the world. Don’t you think if she was abducted for a childless couple her life would be anything but normal as the couple would have been terrified from the beginning that she may be identified? Do you really think that any couple knowing of the circumstances surrounding how the child was obtained and the worldwide publicity that ensued would be prepared to accept that child ?
It seems from your post you are talking about an individual(s) procuring a child for a childless couple? My thinking is that a childless couple actually carried out the abduction with a view to raising MM. If I'm right then the couple could not possibly have envisaged the media circus that followed. Had they have done they might have thought twice.
What exactly did media coverage amount to outside UK? A lot of people live in their own worlds and simply don't watch/read the news. Even if I assume it was media saturation across Europe it only went on for so long until people turned off and became desensitised to all the 'sightings'. By which time MM was developing fast and her physical appearance changing.
If you Google 'Madeleine McCann images' I don't think you will find any with her hair up in a pony tail. Even doing this would throw most people of the trail.
https://www.google.com/search?q=madeleine+mccann+images&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi2z_eds7vjAhWHi1wKHe6eAx0Q_AUIECgB&biw=960&bih=536And it would depend on the couples lifestyle. If they were your typical Mr and Mrs Jones living in a community where they were known with regular 9 - 5 jobs, extended family and social circle then it's difficult to see how they could incorporate MM into their lives without keeping her hidden. But maybe their lifestyle was more flexible and open and they were able to all fall under the radar.