Opening versus end credits. Opening credits are short and selective: they usually bill the principal cast before the crew and end on the director's card. A film without opening credits often starts its end credits with those same roles in reverse, director first, before the full cast and crew. Credits on Wikipedia describes both conventions.
Contracts and guilds. On a union production the placement and wording of some credits are fixed by agreement rather than taste. The Directors Guild of America accepts only Directed by
for its members' credit; the Writers Guild of America decides who may be credited as Written by
, Screenplay by
or Story by
, and how a source-material credit reads. See the DGA on director credits and the WGA Screen Credits Manual.
The possessory credit. A film by
is a separate, negotiated credit, not part of the standard order: the DGA's agreements leave it to individual negotiation and do not grant it on a director's first feature unless the director brought the property. The generator has no slot for it; if you have one, it goes on its own card. DGA on creative rights and credits.
Running time. Credits count towards a film's running time. The Academy's rules treat a film as a short only when it runs 40 minutes or less including all credits, so on a short every extra card has a cost. Academy rules and eligibility.