Good Morning,
I too, have called it a Mille Feuille however, in the USA it is called a Napolean.
Thanks for posting that photo of the Danish Napolean Hat Pastries ...
As English is the 2nd or 3rd language of most Corporate workers, the names of things have been changing and thus, this is perhaps why many things have more than one name.
Another point is that everyone is studying English now; and depending if one´s English Teacher is British or Canadian, American, and lesser Irish or Australian, can also have an effect on the vocabulary and names of foods etcetra ...
Kind regards,
Margi.