birth-death range - person still alive

For a person for whom both dates are known, use the form “1923–2003” (preferably, per CMS, with an en dash, not hyphen, double hyphen, or em dash); for one still living, just write “b. 1923.”

For a person still alive you write (1955-); for a person who has died you write (1955-2012). Make sure you don't put spaces around your hyphen. Their dates should count as one word only in your essay count. (Source: I'm a uni student and have written a few essays by now).

Now I'd like to know what you put if you can't find their year of birth anywhere online or in books! (N.d.) or what?? :(