O SOLE MIO is no longer a PD song due to a ruling in 2004 by a judge in Torino. His ruling stated that Alfredo Mazzucchi (1878-1972) deserved to be listed as a co-author of that song, along with the traditional authors, lyricist Giovanni Capurro (1859-1929), and composer Eduardo di Capua (1865-1917).

Mazzucchi had been long referred to as a "transcriber" -- a young musician who would work at the piano to help songwriters get their ideas down onto manuscript paper. His descendants claimed that he had had as much to do with many of di Capua's famous melodies as di Capua, himself. Evidently their proof of the claim was compelling, since the judge said in his ruling that Mazzucchi's contribution to the "creative process" was "indistinguishable" from that of di Capua, the person traditionally regarded as the composer of the melody. 18 other popular Neapolitan songs composed by di Capua fall into the decision (including Maria Mar aka: Marì).

These 18 songs, including O SOLE MIO will not come back into the public domain until at least 2042.

Cheers!
Gael