Nice shot......looks to me (my opinion) that it might be some corrosive damage......now I could be wrong (I am lots of times) and it's hard to say why the corrosion would be limited to a certain digit, but the discoloration around it (digit) leads me to believe that. Others more knowledgeable will chime in.......
2001 with some rot. Far from rare or valuable other than face. Also, and just as a friendly FYI, only one thread is necessary.