If you think about it, Social Security really doesn't really need to care that much what your birthday was when you are working and paying taxes into the system. When you retire and want to collect benefits is when things would change. If you don't have proof of age at that point you may need to go through some hoops to prove your age & eligibility. So it makes sense there could be millions of people in there with a day 0 since the epoch age. Also, don't forget millions of undocumented workers have a SS# and won't be collecting any benefits later.