I have a friend that is an accountant. She gave me an update that the IRS put out to answer this question. I don't have it with me it is at work but the best I remember is that you actually have up to two years to readopt in your state and take the credit.
Granted most people would want to take it ASAP (the year you come home with the child) but in our case we were wanting to know how/if we could delay. We have a rental house we were thinking of selling so we didn't want to go over the income limit for the year and not be able to use the credit.
http://www.mellon.com/hris/pdf/fyi_07_19_05b.pdf
The above link gives the new guidance on when an adoption is final.
Cindy