Just looked at my P09 .40.
Right side of the slide, in front of the ejection port is the serial number. To the left of the serial number is a number "14".
Makes me think that's the year of manufacture as it's about when I bought that pistol.
Every time I grab/look at that P09 .40 I think, "I really should have had it milled for a red dot and back up sights years ago."
If I did that might put the M&Ps and FNS .40's in the safe for good.