I just checked, Champignoncremesuppe is not in my dictionary ;)

It has some compound words. But including too many of them would quickly get out of hand

but can't you basically make anything a composite noun in German? That it's a single word doesn't really help you decided if it has enough presence unto itself to be defined in the dictionary.

Seems like they would have just as much of a problem since the issue is delineating when a "phrase" becomes a "word"

In Dutch we indeed happily do this even for English loanwords like "creditcard" or something more obscure like "lockpick". When in doubt, remove the space.