In this document [1] dated 1967-68, on page 8, IBM mention 8-bit character sets only: their EBCDIC and the "8-bit extension of the 7-bit code" proposed by ISO.
Because eight rather than six bits are used
to represent a. character, up to 256 possible characters
could be represented in the Extended Binary Coded
Decimal Interchange Code (EBCDIC) shown in Figure 7. Except for certain teleprocessing equipment,
the code that makes use of characters is either
EBCDIC or an eight-bit extension of a seven-bit code
proposed by the International Standards Organization.
Because eight rather than six bits are used to represent a. character, up to 256 possible characters could be represented in the Extended Binary Coded Decimal Interchange Code (EBCDIC) shown in Figure 7. Except for certain teleprocessing equipment, the code that makes use of characters is either EBCDIC or an eight-bit extension of a seven-bit code proposed by the International Standards Organization.
[1] http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/GC2...