'Merlin': Series 4 Episode 7 teasers 

Could anyone explain to me how these teasers work? Multiple sites post them, but they are all a little different. Are they an official release from Shine, or do these sites get script readings or what? Also have seen no spoiler reviews before the show, do these people get early screenings or what? Just curious to know, hope someone could clue me in, thanks.

Well, I know they're official. And that's pretty much all I know.

Thanks MISA.