[jcranmer]

That's not what ©1994 means. What it actually does is it establishes first publication date.

In US copyright law, there are three dates that control copyright: 120 years from creation (first fixation), 95 years from first publication, or life + 70 years. If any one of those terms expire [1], the work moves into the public domain.

Affixing an earlier copyright date affords no advantages. Pre-1976 copyright reform, flubbing the formalities means you lose copyright entirely. After that reform, you still keep copyright, but instead you lose out on some ability to recuperate losses, and you give your opponent extra legal ammunition in any copyright infringement cases.

[1] Strictly speaking, life + 70 years actually rules when the author is determined. If you read the law carefully, once the fixation/publication threshold is crossed, it is now the burden of proof of the copyright owner to demonstrate that life + 70 hasn't happened yet, and furthermore to demonstrate that the alleged infringer failed to do due diligence to determine the death date of the author. In practice, it could end up really being a lesser-of-all-three situation, but we aren't going to get any case law on this until 2074 at the earliest, since life + 70 doesn't start until 1978.