Rogue One: A Star Wars Story, filled in a piece of Star Wars history that few probably gave too much thought, but that ultimately proved to be a story worth telling. In doing so, the film had to create some new details within the Star Wars universe that had never been specifically referenced. It's a difficult line to walk, as the movie tried to create these new characters and references in such a way that they fit seamlessly into the existing films.
One of the film's little tricky moves, is how it retroactively creates the inspiration for Luke Skywalker's Rogue Squadron. We meet the squadron of pilots led by Luke in Star Wars: The Empire Strikes Back, but Rogue One: A Star Wars Story implies that these flyers may have taken their name from Rogue One, the call sign that Jyn Erso's group invents for themselves.
From the first attack on the Death Star in Star Wars: A New Hope, we know that Squadron leader's are simply referred to as that, like Red Leader or Gold Leader. It could be that being Red Leader is simply the same thing as being Red One, but it's never explicitly explained in the movies that this is the case, and so Gary Witta has come up with his own explanation as to why Rogue Squadron doesn't have a Rogue One. The name has been retired, in the same way a sports team retires a number.
While Gary Witta is clear that this is his own reasoning, and is not canon in any way, it's certainly a nice thought. The idea that Luke's squadron's name was inspired by the brave souls who stole the Death Star plans is, of course, a complete retcon, but it's the sort of retcon that works. It makes some sense, and it doesn't fly in the face of any other specific knowledge that the movies give us.
It's also not particularly important information, so if you don't buy it, it really doesn't matter. At the end of the day we all know we're making this up as we go along, and we just choose to accept this sort of thing, or not.
The larger that the Star Wars galaxy becomes, the harder it's going to be to fit the pieces together. The expectation is that the next set of movies will take place far in the past, perhaps hundreds of years before the prequels, which will open things up a bit, though there will still be existing details that may need to be worked into the story.
What do you think of Gary Witta's own fan theory? Does it work for you?