I went back through the videos from the Pokemon channel for XY and SM. There's actually a lot of timing overlaps between them. Need to do 2 posts cause SM was PACKED.
Again, this is just videos, not Corocoro. Corocoro probably had the same info around the same time though.
>January 8, 2013 - Pokemon X & Y Announced, Gameplay Shown, Chespin, Fennekin, Froakie, Xerneas & Yveltal (shown but not named)
>February 14 - Sylveon (didn't say the type)
>April 6 - Mega Mewtwo Y (didn't explain anything about it)
>May 14 - Riding on Gogoat, Lumiose City, Fletchling, Pancham, Helioptile, Gogoat
>June 11 - Sky Battle, Talonflame, Clauncher, Skrelp, Horde Battles
>June 14 - Shauna, Tierno, Trevor, Serena, Calem, Gyms, Viola, Scatterbug, Spewpa, Vivillon, Flabébé, Litleo, Noivern
>July 12 - Sycamore, Inkay, Malamar, Pangoro, Slurpuff, Spritzee, Team Flare, Xerneas, Yveltal
>August 9 - Mega Evolution, Mega Mewtwo Y, Mega Lucario, Korrina, Bunnelby, Dedenne, Skiddo, Torchic Giveaway, Mega Blaziken
>August 11 - Mega Mawile, Mega Absol, Mega Ampharos
>September 4 - Kanto Starters in the Game, Mega Charizard Y, Mega Venusaur, Mega Blastoise
>September 13 - Quilladin, Braixen, Frogadier, Tyrunt, Amaura, Character Customization, Furfrou Styles, Meowstic, Pyroar, Mega Garchomp, Mega Mewtwo X,
>October 2 - Mega Charizard X
October 2 - Final Evolutions of the starters leaked via screenshots of the game
>October 12 - X & Y Released
Yes, there actually was never a video for the XY starter final evolutions.
