Although the ASCII committee thought of ` as a diacritic and ' as an apostrophe, the Unix tradition was to treat them as left and right single quotes (the characters that are now in Unicode as U+2018 and U+2019). This is most obvious from the TeX convention that you write ``quoted text'' in the markup source and you get “quoted text” in the formatted document.

As such, ` and ' were considered each others' inverse, and ´ was not felt to be missing.

Although the ASCII committee thought of ` as a diacritic and ' as an apostrophe, the Unix tradition was to treat them as left and right single quotes (the characters that are now in Unicode as U+2018 and U+2019). This is most obvious from the TeX convention that you write ``quoted text'' in the markup source and you get “quoted text” in the formatted document. This can also be seen in older monospace fonts, such as the bitmap fonts shipped with X11R5 and X11R6, where the two characters were given mirror-image glyphs.

As such, ` and ' were considered each others' inverse, and ´ was not felt to be missing.