The editors of The Bluebook provide a great FAQ page, Blue Tips. Organized by topic, the page explains puzzling questions such as "When is it OK to use the abbreviation "U.S.?", and "How do I cite an act that forms part of a broader statute?". If you don't see the answer to your question, submit it to the editors. If they think the answer would be useful to others, it could become the newest Blue Tip.
Thanks to Joe Hodnicki at Law Librarian blog for his post on this resource.