RX-7 'names'

The third gen, FD3S, was the Efini RX-7.
The second gen, FC3S, was the Savanna RX-7.
What was the first generation? Did it have a name?
And how did they get to the letter 'D' for the third one? Were 'A' or 'B' missing?

79-80 = SA
81-85 = FB
86-91 = FC
93-95 = FD

Is the difference between the 79-80 set and the 81-85 set the split taillight set? They're both first generation right? Or am I counting wrong?

Welcome to AF, by the way. :)

Theyre both the first generation, and the tail lights are different. Many interior changes were made between 79-85.