It seems that Gareth Edwards felt that the best way to remove pressure associated with making a Star Wars spinoff, according to these comments during a Reddit AMA, was to remind himself regularly that the previous attempts were pretty terrible.
While Rogue One: A Star Wars Story was the first theatrical spinoff of the franchise, it technically wasn’t the first ever.
It was a 1984 television movie that focused on the fuzzy creatures introduced in Star Wars: The Return of the Jedi.
Whether or not the Star Wars Holiday Special counts, Caravan of Courage: An Ewok Adventure certainly would.