1850 was the year his birth was recorded in the bible as 1809. My own great grandmother had 3 different birth years in 3 different censuses. After all they are taking your word for it. Apparently she wanted to be younger and so did Abe.
I am just taking the word of people who knew him as a young boy and knew he was older than was reported when he was older.
Read Herndon's, Cathey's and Coggins's books. You might be surprised.
I say it doesn't matter to me because it really doesn't. If you celebrate his birthdate in 2009, it is not my concern. I will not. I research for my own benefit and to satisfy my own curiosity.
Have a wonderful evening.