In the history of the Academy Awards, "Best Assistant Director" has never been a category.
When the awards ceremony began in 1929, there were only twelve categories, some of which included Best Picture, Actor, Actress, and Directing awards.
The Best Supporting Actor and Actress categories were introduced four years later in 1933.
Best Story was also a category in the early years of the Academy Awards, but it was discontinued after 1956. However, in 1969, it was reintroduced as the Best Original Screenplay award.