I think it has been "refreshed" with a vibrating pen. The serial numbers on these winchesters are notoriously lightly struck and there is a lot of wear that happens right at that point. It is a very dumb place to put a serial number anyway since tangs are often swapped (is your tang original to the gun?). So, my guess is someone wanted it be be a bit more easily seen and they went over it with the etching pen.
Thanks, I looked at it a lot closer with a magnifying glass and you are absolutely right.
