Re: Can anyone identify this device on this flintlock pistol???
Those pictures do cast doubt on the originality of the pistol. Note that the rear of the lockplate inletting was clearly intended for a different shape of lockplate, the muzzle end of the stock has been cut away for a different style of front band, and the poor fitting of the trigger guard. When was that done? Quite possibly in the long past; the "inventor" of the pan cover may have acquired what was then a put together gun to work with, or someone may have put an experimental lockplate on an old gun that happened to be handy.
I see no means of tracing the origin of the gun, and can only say that unless someone turns up a patent or a description, we will probably never know where the gun came from or whose idea the cover actually was.