[fanf2]

ASCII 1963 was the first version of the standard and it lacked _ https://dl.acm.org/doi/10.1145/366707.367524

The 1965 draft had _ https://dl.acm.org/doi/10.1145/363831.363839

The first standard edition with _ was 1968 https://www.rfc-editor.org/info/rfc20

The 1977 version is also available https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub1-2-197...