I have a postage machine at the office and can put any date on an envelope that I want to. The only full and legal protection in the United States is to register the work at the US Copyright Office. Also, registration of the work at your P.R.O. is good for the files. Sometimes publishers decide that copyrights are not, as a matter of policy, registered until their first release date. This does not mean that they are not fully protected under the copyright law.
Registration is only there to help in the case of an infringement and subsequent suit.
All rights reserved.