Waiting would have been a huge gamble. The fact all this stock is left over and a big deal has occurred is pretty much unprecedented with GOTY. I think one of two things has happened this year:
1. Isabelle in general was not a big seller and did not do well; or
2. They are so used to the GOTY dolls selling out early that they upped their stock of the merchandise this year and have far more than usual.
DD has been getting the GOTY dolls since 2010. She also gets a lot of their furniture, accessories etc. She gets the previous years for her birthday in February, some from DH and I and the rest from other family members. This is the first year that I have every seen pretty much everything still available this late. I have NEVER seen this type of deal on the GOTY so that tells me either she was a rotten seller, or they have far more stock than they have ever had in the past. Usually the doll and its stuff are going at premium prices on EBAY before Christmas. I have been tempted more than once to sell the GOTY stuff I had put away for DD because of the high EBAY prices, but she would not have been happy with me.

This year, DD did not really show an interest in Isabelle for most of the year- as it came down to the end of the year she decided she did want her (I think more for the fact that she won't be available after this year than that she really actually wants her).
In my experience, we have had to get things by mid-October or risk a big sell out. Lanie, DD's first GOTY doll, had a trailer. It was all I could do to keep myself from selling that thing on EBAY because it went out of stock and towards the end of November it started selling for $1000 to $1,500 on EBAY. I restrained myself, and 4 years later, that is one of the items that DD still plays with quite a bit. It is probably her favorite. Kanani had a snow cone stand. I had bought it in September, and we had a trip to a town with an American Girl doll store in mid-October and I was looking at it and the clerk came up to me and told me if there was any chance I wanted it that I should get it right then because they were already out in the warehouse, and were pulling from store stock to fill orders, that other stores were already out and were calling to pull from their store for people that wanted them, and that they only had 3 left in their store and then they would not be able to get any others once those were gone.
I'm not sure why Isabelle does not seem to have much appeal. DD is 8 now, so I attributed her lack of interest to just being about aged out of them (which is funny because the age on them is 8 and up- but most of the girls I know are into them from about 3 to 7, and then not so much. DD doesn't play with them nearly as much as she used to). DD likes dance and fashion design, and a lot of kids we know do also, so I would have thought that Isabelle would be pretty popular. I think maybe it is that she is too similar to the average kid and doesn't have anything adventurous or different about her?