Well, it's the same authentication problem of validating US citizenship without documentation. And the passport I was issued was in no way a backup, it was vali

Well, it's the same authentication problem of validating US citizenship without documentation. And the passport I was issued was in no way a backup, it was valid for the normal 10-year period and, apart from the note that said it was issued at the US embassy in Madrid, identical to one I would have been issued through the normal process inside the US.