While factory mis-marks aren't common, they do happen.
The barrel marks are applied with a roll stamping machine that rolls a hardened steel wheel with the stamp engraved on it over the barrel and presses the stamp in.
What can happen is the roll die is damaged and they don't catch it, or the die may have been accidentally lifted off the barrel for about a letter's worth.
I'd guess you have a one of a kind mis-mark Trooper.
This probably doesn't increase the value, and would probably decrease the value unless a collector who collect mis-marks would buy it.