Dear Harry,

I cannot speak on behalf of the Library's rules as I am not affiliated in any official way.

But speaking from personal experience, I am an American doctoral candidate living alternatively between California and Kathmandu and I have had no problems ordering digital copies through the Staatsbibliothek zu Berlin. In fact, several years ago before they created the online webshop, one previously had to email a librarian directly to request a copy. Back then, when I first reached out to establish a relationship with one of the librarians, I even stated clearly in my introductory email that I am an American grad student and she made zero objections.