>The events of FR/LG take place. The events of Sapphire begin to take place, however.
>Team Aqua succesfully utilizes Kyogre's power to flood most of the Hoenn Region.
Half a Year Passes
>Team Aqua is defeated by the first Player Character in the Kamla Region, Archie gives up along with his Kyogre. (Pokemon Alchemist GBA)
>Black White Takes Place
2 Years Pass
>Black/White 2 Takes Place
A Year Passes
>Pokemon Alchemist Essentials takes place.
>The events of HG/SS and Platinum take place.
None of this matters at all, and the story can be enjoyed regardless of timeline information but this was made just for convenience.
The only changes regarding the official canon is how Sapphire concludes, and BW/BW2 placement. Gen 6 never happens because I don't like those games.