Ok Miss  Weird, same thing  happened to me too.One of my teacher  for  some reason  entered wrong  birthdate on my  SLC  papers.And as u said   since that  day  i have been celebrating two  birthdays.Btw we  do get a day off  on our birthday at my  work place, and i recently got off  on my  fake birthday.So each year i celebrate  my  birthday  with my  collegue and my  family but  on different dates:)