It's like the apocryphal 13th floor in hotels, people should be born in either 1968 or 1970. Otherwise I might make a fool of myself by mocking their username.
In fairness, if I was born in 1969 I would be deeply torn between using it in every single username I had for the sake of comedy, or avoiding it precisely because people tend to make assumptions and actually being born then is never going to be anyone's first thought.
Original comment follows:
The lawyer who sent the letter has the wikipedia username "kimlynn69".
You'd think that a lawyer, engaging in actions on behalf of a client, would use a more professional username.