Talking US law here.

The above advice regarding the restriction of copyright proceedings in the absence of US copyright registration is only valid in the case of "United States Works". See S 101 for the definition of "United States Work" and see S 411 for the restriction.

It does not affect most (a) works of non-US authors nor (b) works first published outside the US.

I had been worrying that that which was stated above was not compatible with the Berne Convention, and sure enough the genesis of the amendments (although not he current text) came from the (US) Berne Convention Implementation At.