Yeah, Neil is trained by Washington in the future after Washington sets up the Tenet organization. Thus he would have had to have inverted for a few years in order to meet Washington at the time of the movie.
Now it's possible Neil's done hundreds of missions that have cumulatively added up to a few years of inversion, but it's still a stretch.
- You may be a Republican, I'm a Democrat, but we can still be friends. I'll hug your elephant, and you can kiss my ass.