I would not sweat it too much. This damage is common and seems to happen when people try to force non-rotating keyed spacers to "unscrew" when adjusting or removing the headset.

I have had really good luck just cleaning up the *remaining* threads and using the fork as is. The threaded components still go up and down all right once the threads are cleaned up, and since the stripping occurs where the spacer goes, there's usually adequate threading left for the races and locknut to seat.

PS now I see [MENTION=84826]randyjawa[/MENTION] and [MENTION=9425]madpogue[/MENTION] have already pointed this out more precisely and accurately