Advertisements are only permitted when they are directed by a person who has directed or produced a full-length series or movie.
Example 1:
Kyoto Animation: Ajisai-hen is a commercial directed by Shoko Ikeda and produced by Kyoto Animation.
Example 2:
Taisei Kensetsu: Sri Lanka Kousokudouro was directed by Makoto Shinkai, who has directed multiple full-length movies.