trilogy
noun
a group of three related novels, plays, films, etc.
3 films by the same Director, in the same genre, with the same focus of political satire, counts.
As does 3 films from stories by the same author, especially when two are linked by being prison stories, two are from the same book and all are told through flashback, use of narration and examine topics of crime, guilt, innocence, race and justice. All are set in mid 20th century America with SBM and Shawshank overlapping.
The beauty of art is that it’s the watcher that gets to decide what they think. It doesn’t have to be Toy Story 1,2 and 3 to count.