Confused about what can happen?

I am new on this forum and I am trying to figure out legal issues. My heart goes out to all of you who are suffering a failed match or contested adoption. I will keep you all in my prayers. In your cases where the adoption is contested is it a foster care placement or is it before TPR's were signed for both Bmom and Bdad. I am just confused on what can happen before an adoption is finialized. I was under the impression that after TPR's were signed it was a done deal unless the adoptive family was found to not be a good match? Was this false information? All answers welcomed.