Fugi, that's like saying the P-47D11 and P-47N are the same plane, and the B-25C and B-25H are the same.
The P-39D and P-39N are very different beasts. About as different as a spit5 is to a spit8
New ones include wirbelwind, P-39D, P-39N, Halftrack, and at this rate who knows what's next?!