on the serial number list I saw the following under the PSP list:
17851 - IB - 1981 - XX - 9mm - ex-GSG9 gun, issued to elite West German anti-terrorist unit Grenzschutzgruppe 9
I have a PSP whose last two digits are a very few off of this one, it came from the estate of a gunsmith who worked at STI. any light shed on this particular lot of #178XX PSPs with IB code would be appreciated. thank you!