I have just got ahold of a used Gold Cup NM blued Mk iV Series 80. Serial is FN011(XX)E. IF I run just the FN and the 5 digit number thru Colt site it says that the production date is 1983. If I run it with the E on the end, it is blank. I was wondering if anyone knew the significance of the E suffix. Odd thing is that it has the Colt medallion black wrap around grips, that look to be factory grips. Noticed they are copyrighted 1990, named "Radical Grips" inside. So that seems odd, as they look like they have never been off the gun. Find them fugly and put on some nice checkered rosewood I had around.