> because their DoB's aren't public knowledge anymore

Most are on Wikipedia, no?

Even if they weren't, most MPs will be old enough that their top level Birth Records are available, so if they don't have a common name or you know enough biographical details you can find them anyway. If they've got a weird name like Elon Musk you just go name -> DOB in one step, if they're a Sarah Black maybe you need to know approximate age, birth name, rough part of the country where they were born. For super common names like John Smith you will need to know the mother's name, year and specific location of birth at which point yeah you're closer to just knowing their DoB anyway.