As you said they know the autumn colours by know (infact I would imagine they are on Autumn 2015 and beyond).
well butler and wilson always says he's working way into next year or the year after, and he only does jewellery (on a rather small basis - compared to other companies), i would assume for bigger brands that are required to make millions of units, they know far ahead of the time in order to have them all designed, made and shipped out ready for the autumn.