The Wire has a lot of little anachronisms in it due to the fact that it was based on material that was written from David Simon’s experiences in the 1980-1990s. The show creators chose to leave some of that stuff in, even though the TV show was set in the early 2000s. So you have cops using manual typewriters, people using pagers in the first season, etc. Possibly Omar Little’s birthdate is another one of those things.