PC Gamer: "The unfinished preview build had plenty of bugs, which explains the recent delay for polish. The griffon chase twice ended with the griffon flying inside a hill where he couldn't be hit. The horse struggled on uneven terrain. All the guards in Skellige castle started randomly attacking Geralt after a cutscene. There's a chance these will be fixed before release, but we're praying The Witcher 3 doesn't become the next Assassin's Creed: Unity. Luckily the screen-tear you might read about in other previews didn't apply to the PC version, which looked beautiful throughout."
Delay was for general bugs as CDPR said. No graphics optimization here.
Last gameplay and Sword of Destiny show differences, not huge but, some textures are lower in vegetation, lighting looks a little lesser quality and looks like the first trailers and gameplay had some post process effect like "sweet fx" or some shader reduced color saturation and making some more contrast and shadows.
If i'm asked, adding Parallax Occlusion Mapping to the ground and some sweet FX preset that uses 1fps only, this game could look Better than ANYTHING in gaming history. I don't know why developers keep making videos with some cosmetic post process effects that later make controversy and complains, rightly done ones.