The same justification exists in JS (where it's copied from Java which copies it from C). However, interestingly checking the FORTRAN IV specification documents for the PDP-10, it's not implemented as a 3 letter ASCII abbreviation. That document dates to 1975, I don't know if I can find if the date exists in the first version of the document, which should date to 1967. I was unable to find a reference to a builtin in the base FORTRAN II, which only provides 20 builtin functions, date not making the list. I think newer versions of FORTRAN77 has idate which is 1-indexed but I couldn't find it in the older standard listed on wg5's specification documents.

[^1]: https://github.com/PDP-10/f40/tree/master/doc