Some data sources provide a full birthdate, while others provide only a birth year. In the case of data sources that only provide a year the data may be entered as 1/1/year by default. For example, you may see one entry with a birthdate of 3/4/1963 and another with a birthdate of 1/1/1963 who seem to be the same person. This is because data is not merged if the birthdates are different. Please use your best judgement as to whether this seems to be the same person.