I would be glad to help, but the public-domain-ness of the few scores I have examined is obscure! Example http://hdl.handle.net/1802/4714
does not have "PD-US only" in this list. The composer Rudolf Friml (1879 - 1972) is probably PD-US only. And the page says Copyright © This item is protected by copyright, with all rights reserved.
Please could an Administrator provide the list of the PD-everywhere " Sibley files?
Thanks for the interest in helping out! If only there was an Administrator who could tell us which links are PD-everywhere!!
The entries marked "PD-US only" are links that I or someone else have already checked and found to be not yet public domain for the Canada server (like 1802/4714). So we then edit the page and mark the link as "PD-US only" and go on to the next in the list. Nobody has looked at any of the unlabeled/untagged links yet, so those are the ones that need need their PD-status determined.
Also, the "This item is Copyright ©..." can be ignored as you should instead always verify the PD status based on the composer/editors year of death (Google saves the day when Sibley doesn't list the dates for the composer). The Sibley Library puts that copyright note at the bottom of every file in its system (PD musical scores is just one part of the online system) so it doesn't actually have any relation to the particular score. Our job is to determine the PD-status for the link though it is almost always at least PD-US for it to be in SIbley's online collection.
If you find a link that is PD-everywhere then upload it (The ones you already did look perfect!) and delete it from the list. Otherwise leave it on the list and write a little note next to it about why it is not PD-everywhere yet.
I've been working through the 4000s one by one so at the moment but feel free to jump in anywhere on any of the lists!
Does it make sense now how to go about this? Please let me know if you still have questions.