You are correct. Think about it , you have the following.
XP-38, YP-38, P-332-I, P-322-II, P-38, P-38D, P-38E, P-38F, P-38G, P-38H, P-38J, P-38L, P-38M
F-4, F-4A, F-5A, F-5B, F-5C, F-5E, F-5F, F-5G. Many of these were modified in the field to adapt to needs on the battlefield.
Droop Snoot, Pathfinder and Elint.
Post war maping, air racing, weather research.
My goal is to have at least one of every version.
Mike