If the data base existed, the country associated with a particular network address could be determined, and users could boycott works from nations that failed to enforce a valid ratings system. This loss of an audience would encourage legitimate content providers in foreign countries to press for legislation on false marling similar to the one proposed here. Because there will always be people who don't want to follow rules. There are those who take pleasure in flouting convention, or who feel that, as a matter of principle, the Internet should have no rules. And if even a small number of providers misrate their content to get around filters, the information necessary for filters can't be trusted.
Criminal sanctions are, unfortunately, the only guarantee.
The Communications Decency Act was based on control of content and consequently ran afoul of the First Amendment. It would simply require that content providers, if they choose to rate a work, do so honestly. Anyone can define a ratings system and subscribing to it would be a voluntary affair. These factors should be sufficient to allay First Amendment fears. Anyone would be able to opt out without penalty, albeit at the loss of some portion of their audience.