Did you know that the Library of Congress, Copyright Office, Washington, DC can fine you if you publish a work in the U.S.A. and don't send them the mandatory deposit? For instance, if you publish a hardcover book, you must send them two copies of the best edition within three months. Who knew? This mandatory deposit requirement has nothing to do with copyright registration for your book; it's a separate program. I also learned that, although your rights under copyright law do not require registering with the Copyright Office, you will lose certain benefits should you have to defend your rights in court and you are not registered: 1) you may have a weaker case 2) you won't get an award for damages (just get loss of profit) 3) you won't get your lawyer's fees paid. I'm simplifying, so it's worth reading up on it yourself.
It gets even more complicated when you consider that the Library of Congress also runs the cataloging program for works that might be widely retained in libraries. Again it gets complicated because there are two programs that are mutually exclusive. If your pre-publication book doesn't qualify for the Cataloging in Publication (CIP) program, it's likely qualified for the Preassigned Control Number (PCN) program. If you're in the CIP program you must send them a copy of your book immediately upon publication or your publishing company will be disqualified from participation. If you're in the PCN program, you also must send a copy upon publication, but I didn't notice a deadline or penalty. Mind you, I've simplified the requirements--mass market paperbacks and ebooks don't qualify. Just be aware, you'll owe the Library of Congress three hardcover copies for two different programs.