(too late for me to edit; took me a while to find online)

Another good source on the design of ASCII is Inside ASCII by Bob Bemer, one of the committee members, in three parts in Interface Age May through July 1978.

https://archive.org/details/197805InterfaceAgeV03I05

https://archive.org/details/197806InterfaceAgeV03I06

https://archive.org/details/197807InterfaceAgeV03I07