70 71 a b e body drivers side bucket seat core

CudaJunction said

Needing a drivers side bucket seat used in all a b e body cars 1970 and 1971. 72 - 74 will not work. FABO

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Since I'm totally ignorant on the subject, what is the difference between the 70-71 and 72-74 seats? I thought they were all the same.:???: