It was thus said that the Great Noel Chiappa via cctalk once stated:
"The [8008] was commissioned by Computer Terminal Corporation (CTC) to
implement an instruction set of their design for their Datapoint 2200
programmable terminal. As the chip was delayed and did not meet CTC's
performance goals, the 2200 ended up using CTC's own TTL-based CPU instead."
The 8008 was started before the 4004, but wound up coming out after it. (See
Lamont Wood, "Datapoint", pg. 73.) This is confirmed by its original name,
1201 - the 4004 was going to be named the 1202, until Faggin convinced
Intel to name it the 4004.
I found this Youtube video
https://www.youtube.com/watch?v=g9_FYRAfyqQ
about the register set of the 4004, 8008, 8080, Z80, 8086 (and so on) to be
interesting. I don't think it's 100% accurate, but it gives (in my opinion)
a decent overview of the history of the x86 register set.
-spc