Resident Evil Gaiden/development

Canonicity
The plot point of Leon joining an underground anti-Umbrella organization was referenced in Wesker's Report. However, the game was never considered part of the series timeline ("canon") by the writers of the series, despite a statement from Hiroki Katoh (who also wrote Wesker's Report) implying as such. At the end of the game, Leon is killed and impersonated by the "B.O.W." Overall, the game is a "what-if" side-story and has no bearing on the canon.

Resident Evil: The Darkside Chronicles further omits the incident aboard the Starlight. When Jack Krauser told Leon to tell him everything about his experiences with zombies and BOWs, Leon only mentioned Resident Evil 2's events.