Looking at the statistics page for the migrated questions, I read the word rejected. Does that mean it is possible to reject a migration before it is done, or it is referring to the questions that have been migrated, and then closed?
Migrated and then subsequently closed or deleted. It lets us see if there are any giant problems (for example, if a site migrations 30 questions and 90% get closed, we need to have a talk with them about when migrations to us are ok). But it doesn't really affect us since we don't get so many migrations.