I have a FAA issued pilot license and section VI says: Nationality - USA.
This is a federal agency written certification attesting to
my nationality.

When I became a US citizen, I sent the required letter of notification
to Oklahoma city. Several weeks later I received my new certificate with
"Nationality - USA" on it. At no point did I submit any documentation
proving that I was what I said I was - they simply took my word for it.
Hardly "written certification attesting to my nationality", IMHO.

Tony V.