Hi Rebecca,

You don't say what records you have seen.  It was common for people (even some born in the U.S.) to not know their exact birthdate.  My grandfather, who came to the U.S. as a young child in 1892, wrote in his diary in 1902 that "I be on or over the age of 21."  Hence, he did not know his exact birthdate.  I've seen people whose birthdates on various records change each time, i.e different month, different day, and different year.