>>281138401
Even disregarding that, the fact that Pidgeotto is seen in it proves that it wasn't meant to be set at the end, since Pidgeotto evolving into Pidgeot and fighting Fearow was known from day 1 due to the opening: https://youtu.be/TZMoQjvoICE&t=36

We actually have an illustration of plans for the anime that ended up getting changed, and according to it, Bulbasaur was supposed to have evolved all the way into Venusaur by the league, while Pidgeotto hadn't evolved yet. Between this and the way things come full circle when the fully evolved form of the Pokemon Ash failed to catch in the first episode fights off the fully evolved form of the Pokemon attacking him in the first episode, it can be safely concluded that the anime was meant to end with Pidgeot vs Fearow (and this may well also have been why they decided to save his reunion with Pidgeot for the very final episode decades later, as there are some deliberate parallels to the start in the last few episodes where Ash shows how he has grown when it comes to interacting with the wild Pokemon from the first few episodes).

In other words, the movie was most likely always meant to be set around the 8th gym, as it is in the final anime.