I quote Nathan L. Swayze author of "51 Colt Navies" from a speech given to a convention of the American Society of Arms Collectors (I am unable to obtain a usable copy of the photo):
"The top frame is what I call the "Early Frame" for no improvements have been made. The percussion cut-out is larger and deeper, and it does not have the cap guiding groove. This percussion shield cut-out is more in the lower one-half of the percussion shield, although it doesn't appear this way in the photo due the angle of the camera. The middle frame is the "Late Frame." You will note that the cap guiding groove has been added, and the percussion shield cut-out is smaller, shallower and more in the center of the percussion shield. The bottom frame is the 4 screw cut for stock frame. The primary difference here is the addition of a fourth screw, which is actually a stud for the prongs, or fingers, of the stock attachment. Also, the bottom of the percussion shield has been milled to fit the prongs, or fingers, of the stock."
To the best of my limited knowledge no London Navies had a capping grove. Flayderman's does not have a photo of a Navy with a capping grove but does Say "The number of variations is considerable, all are detailed in the standard reference Work "51 Colt Navies": by Nathan L.
Swayze".