Feltwad, I can say that at some point, some small wood repairs were done (you can see these if you look close on the pictures). They appear neatly done. With regard to the gold fill of the signature on the top flat, it would really surprise me if someone did that (based on cost, etc), but you never know. Someone that was very handy might have had some material that they wanted to dispose of, and had that brilliant idea to fill in the signature. I would say that they would have to have been a masterful gunsmith, based on the quality of the job, and the fact that there are no signs of any interruption on the adjacent surfaces. I would tend to think that it has been that way for a long time. And, I got the fowler at a local gun shop, and it was on consignment as part of an estate sale. It hasn't been groomed to pull premium money or anything, if that makes sense.
I just think that it was a very high grade piece from jump, given the quality of wood, checkering (that is now worn down), engraving, etc. It's very cool that you have restored some pieces by this maker. Would love to hear more thoughts from you, and share more pics if you would like.