I've never heard of a nation's government refusing to process a request for return of a child under the Hague Convention on child abduction, and to let the petitioner then go to a court for a decision on whether to return the child. It must happen sometimes, but you don't tend to hear of it. But the U.S. State Department is absolutely right to do that in the case of Anyeli Hernandez, who was abducted from Guatemala over a year before the Convention went into effect there. "Hernandez, now seven, was abducted in November 2006 and wound up, illegally, with an adopting American couple. ... Guatemalan authorities have prosecuted three people for kidnapping and for placing Anyeli Hernandez up for adoption." ("U.S. will not return illegally adopted Guatemalan girl" - Agence France-Presse, Tuesday, May 15, 2012)
The Hague Convention very clearly says that it only applies to cases where the Convention was in effect between both countries at the time of the abduction. But as the State Department points out, the real mother in Guatemala can still go to the local courts where the child lives to enforce her custody order and undo the adoption. That is not just a theoretical cop-out by the State Dept. - it is something that we and other lawyers do all the time, using a uniform state law, the Uniform Child Custody Jurisdiction and Enforcement Act. It helps many parents in cases where the Hague Convention does not apply.