The claim is birthdate+zip+gender could uniquely identify 87% of the US population, and there are respectable studies to back this stuff up (https://groups.csail.mit.edu/mac/classes/6.805/articles/priv...). There aren't a lot of days where there's only one person celebrating their birthday in an entire zip code.

Even factoring in birth year and gender, I struggle with this a bit, because I know that in densely populated areas of the country, where more and more of the population lives (upwards of 80% of the US lives in urban environments), you'll find multiple babies with the same gender being born in the same hospital on any given day... and there are often multiple hospitals servicing the same zip code!

Despite all this, your point still stands: it doesn't take much data to deanonymize someone.