I found your post about the wording of the copyright laws to be illuminating. I'd never studied them that closely.
Peanuts compared to the Holyoke discussion, since better-versed people than I have already compiled the information. I haven't even given Google much of a workout!
Oh, and the other use of registration is the ability to terminate a grant when the property changes hands before the renewal. That is, if a writer licensed his text for ten years before the end of the first term and died before the expiration, the heirs would only have the option to revoke the license after renewal, and then only if the registration was made beforehand. At least, I think that's what it says.
Anyway, here's yet another twist, from as late as 1977. This might be of interest: "After copyright has been secured by publication of the work with the notice of copyright...there shall be promptly deposited in the Copyright Office...two complete copies of the best edition thereof then published..." (S13). If not? That's S14.
"Should the copies called for by section 13 of this title not be promptly deposited as provided in this title, the Register of Copyrights may at any time after the publication of the work, upon actual notice, require the proprietor of the copyright to deposit them, and after the said demand shall have been made, in default of the deposit of copies of the work within three months from any part of the United States, except an outlying territorial possession of the United States, or within six months from any outlying territorial possession of the United States, or from any foreign country, the proprietor of the copyright shall be liable to a fine of $100 and to pay to the Library of Congress twice the amount of the retail price of the best edition of the work, and the copyright shall become void."
Wait, what?
OK. Copyright comes with only the notice. However, within three months of publication (unless you live far away), you must deposit a copy of the work with the Copyright Office. This was a requirement. If a publisher failed to comply, they'd be fined and lose the copyright. However...that only came into effect if the Copyright Office bothered to pursue it.
To make this more confusing, this is NOT related to registration, which is still optional.
Hm. I wonder if there's a list, somewhere, of those works the Copyright Office demanded but never received.
Interestingly, most of this clause is still in effect, but not the last part. S407 still requires deposit and imposes non-compliance fines ($2,500 plus expenses), but "Neither the deposit requirements of this subsection nor the acquisition provisions of subsection (e) are conditions of copyright protection." It doesn't seem to say what happens if you're billed and still don't comply.
So...uhm...yeah, I got nothin'. And the twists and turns are making my head hurt. I'm getting some fresh air...