Originally Posted by RedTape
Look for a date code (two letters) probably under the front of the slide. A=0 B=1 C=2 etc. That will let you know how old it is.
Not always. It depends on where the gun was produced.
My P229ST frame was manufacured in Germany but was assembled in Exeter, NH. Thus there are no proof marks or date codes.
Nor do my P220ST, P226ST, P239TT have date codes.