It really depends on the laws in your state. For instance, in my state an adoption is contestable 6 months after finalization (only certain things would be considered). After that it is the best interest for the child to stay put (I think is the idea here).
Some of the more publicized disruptions happened due to not going by the book. I think so long as all the bases are covered nothing can happen.
If you'd like to research it go to
www.adoptionlawsite.org (or .com I forget right this sec). You must sign up but they dont send you unsolicited email. In fact, I had to agree to email and the email I get from them is case law and news briefs on adoption (which I now try to stay abreast of). This is a very good site but laws are tedious reading.
I cannot settle your fears fully but I feel certain that after a year you should not worry.
Maia