Federal Appellate Rule 32.1 is now in effect, allowing attorneys to cite “unreported cases” done in 2007 and beyond. Prior to Jan. 1st., the local rules still control.
All federal courts of appeal permit citation to their unpublished opinions in related cases to show res judicata, law of case, and the like. But before 2007, federal appeal courts differed on the extent to which they would allow unreported opinions in cases that were not related. The Fourth, Eighth, and Federal Circuit courts “discouraged” them; and the Second, Seventh, and Ninth disallowed them altogether.
The situation here, on the larger scale, was foreseen by Robert Timothy Reagan of the Federal Judicial Center, who compiled an overview report on each jurisdiction’s position on unreported cases prior to 2007. It’s available here.