Not sure if this is the correct place to post a question like this - if not maybe the mods can move this.

It arises from me trying to decipher a particular airport code in my passport from a CBP stamp - I think it was INS back then. I believe I entered the country at DTW but since the stamp is partially obscured I cannot see how it could be DTW.

Looking at other stamps I have in my passport some of the other POE stamps include SDP, LOS (which I think was LAX), WAS (which I believe was stamped at IAD) and VCV (which I believe is YVR).

Can anyone shed any light on why the CBP POE designations are different to the IATA codes and is there a translation from one to the other? That will hopefully help me decipher the stamp in question.