First off, AMD 103 stands for Amtrak Diesel--Top speed 103mph, for all you who didn't know....
Anyway, when the P40s first came out, I think they were called AMD 103 "Genesis". Then the P42 came out tand they went 110, so they renamed the first to P40 and the second became the P42, because they were a little different. But...You can call em whatever you want.
Joe