While he may not have known her exact age or the date it is more then likely that he would have know Neely's history of attacking people on that line if he was a regular traveler on that subway train.
Neely was notorious among the people who rode the subway.
It is a common misconception that people who are ride the subway are just a faceless mass. But when you ride any sort of public transportation on a regular basis you get to know the other people on the transport at least by sight.
You may even strike up conversations with some of them and even become friendly. And you get a group of people together they will talk about the news of what is going on in their little world.
Commuters will ride the same train day after day for years. The panhandlers will ALSO ride the same trains day after day, getting on the train where they live, riding it for a while, then getting on the train going back.
After a while you recognize the "regulars".
I’ll take your word for it. It make sense. I’ve only been on one a handful of times.