Neal, I disagree with what you've said. As Read's reply and Jeff's post point out, actually, contra dances might not be considered dance choreography under the statute. And, if I were a judge looking at it, I'd say it isn't. Contra dances might have one or two unique moves, but that is much, much less original than choreography of a ballet, etc. My reading of the statute is that Congress meant the latter, not the former, particularly given the exclusion of social dance steps.
But, I'm not sure about that reading, and my point in emailing is to say that you shouldn't be sure either. As Read mentioned, this is the kind of thing we don't know for sure until somebody decides a case (it would be a judge, not a jury, but that's beside the point). I'd caution everybody on the list, particularly non-lawyers, from giving legal conclusions and saying things like "it is correct based on the law." Neal, your conclusions probably aren't correct, but maybe they are. I don't practice copyright law, but even if I did, I highly doubt I'd know a sure answer.
But one thing your post points out is important to keep in mind. You can only sue for actual damages if the copyright's unregistered. From this, I take two points. One, since I'm not aware of anybody ever registering a contra dance, it's very unlikely that anybody would be able to show sufficient harm from somebody else's use of that dance to actually win a case. So, it's totally not worth suing over. Two, sometimes people sue over things that are not worth suing over, so it's probably also worth it to make a minimum effort to contact dance authors. It doesn't hurt anything to do so and only takes a few seconds. I'm not aware of any dance caller who has asked somebody not to call their dance. Publish, sure, people might not want you to, but call it? That's why people write dances.