École Polytechnique students identify their academic year, or "promotion" in French, by start year date.
For example, Ciro Santilli's year started in 2009, though as a foreign student he arrived only at the start of 2010, and Ciro's promotion is usually known just as X09. And as the century barrier is broken we'll start to need to specify as X2009 one day.
List of notable alumni:
- fr.wikipedia.org/wiki/Liste_d%27élèves_de_l%27École_polytechnique This French list is a bit better as you'd expect
- en.wikipedia.org/wiki/List_of_%C3%89cole_Polytechnique_alumni