>If it's from somewhere outside the US, then you ain't eligible to vote anyway unless you've gone through the process of becoming a naturalized citizen

It's nitpicking, but you can be a citizen by birth without either having a birth certificate from a country you are citizen of and without naturalizing, but you will have some other document in that case too.

>Against the state's voter registration database, usually maintained by that state's Secretary of State or equivalent.

Isn't it circular? To be in the database you are checked against the database?