As someone who has over engraved or re-stamped a lost or unclear serial number about a zillion times in the past on a zillion types of kit, ranging from Fazakerley Stens to riflees and bolts and magazines to Kershaw binoculars I'd say that this is what's been done here. If you were at a workshop with an engraving facility handy (called the A&G section) then you'd use it. If you're going to re-engrave, then you should linish clean first