Right. This is a family show, after all...
Meanwhile, getting back to the original topic, for those who care. I took my questions and found an contact page for the folks at the Library of Congress. Good news is they got back to me quickly. Bad news is they decided simple factual questions ("where would I find a list of works whose deposit was demanded?") were "too complex" for e-mail, and directed me to their phone number.
That, admittedly, weirds me out. "This might be too complicated to type out whenever we have free time, because you're not a priority, so let's get together on the phone so that we can dedicate a resource to answering your questions live when he or she could be doing normal work" doesn't quite follow for me...
Even so, I'll give it a shot during the week and see what I can squeeze out of them with regard to the deposit requirements.