The original release date was June 25th 2020, but due to Covid-19 the production was delayed, cancelled, then eventually picked up again at the beginning of 2021.
The film was only green lit because of the fans reaction to Six, originally it was just supposed to be a mini series based on the main "I Am Number Four" books.
In early 2020 when the film had just been announced, some test footage was shot where Six takes down a Mogadorian creature in battle using her weather manipulation legacy. Both Six's weather manipulation and the Mogadorian creature were scrapped due to the Director wanting the story to be more grounded and personal.
The film was originally "The Lost Files" but was changed to "The Lost Files: Six's Legacy" so that they could release other Lost Files stories as sequels.