They were very secretive. But from others posts here, I'd say it's safe to say that the N is for .45 cal, the A is for 2007, and the next letter is for the month.
MPanova's M is Jan, and my P is June, so that one is probably not in alphabetical order. I'd say that they keep that one on an algorithm of some sort. (ie. M=1, P=6, etc.)
Perhaps we should just start a thread where everyone calls in and gets the month/year of their gun, and post what month the third letter was for all 2007 24/7 Pros. It would only take 10 more people. Then we could make a sticky thread on figuring out your own manuf. date.