In recent years, the dates are no secret, but the factories represented by the 3 letter codes change every few months. For instance, LRE ENE 09, would be factory LRE (whatever factory that code represented at the time), January 2009.
IMO, I believe they implemented the rotating box code system so consumers wouldn't chase certain factories. Habanos was probably tired of retailers complaining about boxes with a certain code moving faster than those without it. The problem was that the Partagas, Upmann, etc factories would turn out much better product than provincial factories and the consumers knew this so they'd go after them.