You realize a non negligible portion of any population will be mentally unfit or have conditions (genetic or otherwise) which leave them illiterate? Claiming 100% while ignoring that may as well be saying "everyone who can read and write is literate".
If you're taking an honest measure and still claiming it's possible to approach anywhere near 100% literacy you must be advocating for some impressive eugenics programs.
...Or you could just admit the country with (totally not dynastic) heads of state claiming to win 99.93% of the vote might be lying through their teeth...