Carolus very helpfully created two templates, {{WorkPD-USonly}} and {{FilePD-USonly}}. The former is intended to be inserted at the top of every work page whenever the work is PD-US-only, while the latter is to be included in the information for each score that is PD-US-only.
What denotes a PD-US-only score seems pretty clear: something about the score (music, lyrics, cover art) was created by an author who died < 50 years ago, and the score was published prior to 1923. But whether a work is PD-US-only can depend on things other than the composer. For example, daphnis made Schoenberg's Erwartung available at http://imslp.org/wiki/Erwartung,_Op.17_ ... _Arnold%29. The score is PD-US-only because it was published before 1923 and the lyricist, Marie Pappenheim, died in 1966, which is < 50 years ago and hence non-PD CA/EU. But if the lyrics were excluded, the score would be PD CA/EU. Therefore the work itself is not really PD-US-only -- or is it?
Two other examples daphnis made available are Puccini's Gianni Schicchi and Suor Angelica (http://imslp.org/wiki/Gianni_Schicchi_% ... Giacomo%29 and http://imslp.org/wiki/Suor_Angelica_%28 ... Giacomo%29). Gianni Schicchi furnishes a real example of the semantic conundrum at stake: again, the lyrics are the only thing that make scores of this work non-PD CA/EU, given Puccini's death date. If the lyrics are excluded from the score, as in the instrumental arrangements available for that work, then the score can be PD CA/EU as well as PD US. Since it doesn't make since for a PD-US-only work to have a PD-CA/EU score (or does it?), it seems like such a work should not be labeled PD-US-only. Probably only works for which the composer of the music itself died < 50 years ago -- not the lyricist, the cover artist, et al. -- should be considered PD-US-only. Unless we start publishing standalone libretti on IMSLP.ORG.

What do all of you think?
Jonathan