Someone asked me the exact same question over e-mail, and the answer is that indeed it *would* be a pain. However, even though I know it would be hard for people to get their hands on scores over 70 years old in copyright, nonetheless there is one publisher that makes this possible: Dover Publications. Because they reprint old editions, it makes their publication not copyrightable, since under US law copyrighting a public domain work needs significant editorial changes (derivations), something that Dover scores do not have because they are exact reprints of old editions. The publisher copyright only applies when the score is changed in some significant way (ex. retypesetting).
ATM very few people (read: none) besides me are actively submitting scores, so there hasn't been any problems of that sort. Plus, I'm busy like mad (end of semester), so I don't have time to go through all the pages to add such info. I'll do so during summer vacation.