Not sure what point you're trying to make, though: you buy ad placement from Google, not data about people. Sure, you can make the inference that people who visit your site via a Google ad fall into one of the categories you've targeted (though you won't know which one, unless you've only chosen one), but that's it.
You can target all and only all criteria at once so only people who fall into all criteria will see the ad. A variation may target a different group and have its own tracking.
If they see the ad they fall into the category combination I specify. If they click the ad then I known all of that stuff about a visitor because I know which visitors clicked and which found their way outside of ads. If they signup or enter email or anything like that then I know exactly who they are for most people. Even if I have only an email but no name I can create a shell profile and use a data broker to find the name behind the email a lot of the time. Then I have everything tied to a person.
Multiply this times thousands upon thousands of ad impressions across multiple campaigns and you can bud a pretty good database with highly specific data. Sure 100% accuracy isn't guaranteed but neither is it guaranteed through more direct data brokers.
