Upload & Sell: On
Effective Date of Registration
When the Copyright Office issues a registration certificate, it assigns as the effective date of registration the date it received all required elements—an application, a nonrefundable filing fee, and a nonreturnable deposit in acceptable form, regardless of how long it took to process the application and mail the certificate.
You do not have to receive your certificate before you publish or produce your work, nor do you need permission from the Copyright Office to place a copyright notice on your work. However, the Copyright Office must have acted on your application before you can file a suit for copyright infringement, and certain remedies, such as statutory damages and attorney’s fees, are available only for acts of infringement that occurred after the effective date of registration. If a published work was infringed before the effective date of registration, those remedies may also be available if the effective date of registration is no later than three months after the first publication of the work.
The time the Copyright Office requires to process an application varies, depending on the amount of material the Office is receiving and the method of application. If you apply online for copyright registration, you will receive an email notification when your application is received. If you apply on a paper form, you will not receive an acknowledgement of your application, but you can expect a certificate of registration indicating that the work has been registered; a letter or a telephone call from the Copyright Office if further information is needed; or, if the application cannot be accepted, a letter explaining why it has been rejected.
The Copyright Office cannot honor requests to make certificates available for pickup or to send them by express mail. If you want to know the date that the Copyright Office receives your paper application or your deposit, use registered or certified mail and request a return receipt.
This quoted from Circular 40 of the US Copyright office. As stated from the end of the second paragraph, you have 3 months from the date of first publication to register your work. Date of first publication in the case of infringed works is considered the date the copyright holder discovers the infringement. Congress did not intend to give thieves a three month period to publish a work and hope they don't get caught, so that there is no punishment. This is covered under 17 USC § 412, if I remember correctly. The Copyright office considers date of registration, the date they receive all the materials required for registration.