I have to say, I don't really agree with what a lot of people have said about a trend being out once it hits the stores that mass produces it. The highstreet is the area that most normal people can only afford to shop, and they should be entitled to buy what they like regardless of those who say a trend is 'out' once it is mass produced. Once a trend is mass produced, surely it's a bigger trend than ever because of the amount of people that are wearing it?
IMO, a trend is out once Fashion Week for the next season begins, because suddenly no one is interested in wearing their wintery clothes when all the beautiful new summery ones are being flourished in their faces, even if there is twenty feet out snow outside.