It seems every for sale ad that does not contain a date code gets asked shortly thereafter ,"what is the date code?". What is the significance of the date code? Is it just a gauge for how old a gun is? A LOT of HKs seem to be safe queens so I don't see it as a measure of how "used" a gun is. USPs for example are pretty much unchanged since introduction, so what difference does it make if it's a KK or a AF? Just wondering, I almost never see anyone inquire about date codes on other brand guns for sale.