I don't see anything on this that would suggest it is not the original stock. A little sanding and any cartouches are gone.
And that flat part of the stock opposite the lock is SO TEMPTING to someone sanding out nicks and scratches.
Certain parts of a gun tend to get more attention when polishing or sanding is involved, and this is one of them.
With percussion revolvers, it is the cylinder that gets more attention and more polishing - it is so easy to put it on a drill and sand it as it spins!