I just happened to read an article about this last week...
An adaptation is a licensed copy, in this case of a Chanel original. If it was from the 20s then it was a copy manufactured in the U.S. from a Chanel dress, not a toile. Toiles were purchased post war instead of dresses. The process involved an agreement between Chanel and the manufacturer who would knock it off, usually a department store buyer with connections to a small New York dress manufacturer. They would 'borrow' the dress and bring it to the U.S. THe dress was actually purchased from Chanel but had to be returned to Paris after 6 weeks in the U.S. to avoid paying hefty duties which could be up to as much as half the cost of the original dress itself. An agreed number of copies could be made from the dress, usually something around 50 copies, which were then sold through the department store. The label had to read 'adaptation' in order for it to be a legal copy but sometimes a department store would then rent out the dress to other manufacturers to knock off their own versions, although this was rarely an issue for high end department stores because they wanted the prestige of selling the authentic adaptations.
The adaptation label didn't exist in France because of copyright laws and problems with certain dress manufacturers knocking off versions of dresses pictured in magazines or seen at the shows within days, sometimes hours of a fashion show. Paris ateliers were willing to allow adaptations abroad because buyers from American department stores and other places didn't have access to ateliers to immeadiately run off copies. The time it took just to get the dress back to New York via a boat and knocked off in the U.S. and sold meant that there was a delay of several weeks between the dress first being shown and its adaptations. Also, U.S. department store buyers were usually the last to attend the shows. The regular clients that bought couture were first, then the press, then the foreign buyers. So it kept copying down to a minimum.
The whole adaptation thing died with the war. Postwar designers discovered pret-a-porter as a more effective means to make money.
If I remember correctly from the article, an adaptation sold for around 1/4 of the price of an original Parisian couture dress, so they weren't cheap, but they also weren't expensive since $250 to $400 was about the price of a suit of afternoon dress from a place like Chanel at the time, depending on its ornateness -- more for evening wear. Catalogue dresses from the 1920s are priced around $10 - $30, so $65 - $100 for a couture adaptation isn't that much.
