Q:  What do the date code markings on P7 pistols mean?

A:  The date code markings on the P7 pistols signify the year of manufacture/proofing.  Here are the meanings of the two date code letters:

The date coding system is very simple too.  It gets tricky when you start talking about non-proofed products like firearm magazines, but the general rule is thus:

The letter corresponds to the number.  The letter 'J' is skipped for proofed firearms, but is present on magazines.    Therefore, the P7 above was manufactured in "84" or 1984.

HK Inc Arlington, VA ID Date code = 1983	HK Chantilly, VA IE Date Code = 1984
HK Sterling, VA KH Date Code = 1997	Current HK Sterling with the "Warning" label AC Date Code = 2002