how you determine whether a work is in PD or not if the compose's dates are unknown
Research, but there are many cases in which it has proven impossible to determine when a person has died (the determining factor for two of the three copyright jurisdictions that affects IMSLP--Canada and the E.U.). Sources such as MusicSack
, Oesterreichisches Musiklexikon
as well as biographical dictionaries can be helpful. If a work was published in the U.S. it's copyright protection had to be renewed after 28 years and so the renewal volumes of the Catalog of Copyright Entries
can be helpful. If an item was renewed it will often list who renewed it (the publisher for instance) and/or for whose benefit it was renewed (the composer's widow for instance). Also, by searching Worldcat
for any works the composer published you can get a good feel for the earliest and latest dates during which he was active.
As long as the work was published before 1923 we can always move works of authors whose dates are unknown but who may have died less than 50 years ago to the U.S. server since it will be in the public domain in the U.S.
There may be an actual legal framework for determining when a work whose author's date of death cannot be determined enters the public domain but that goes beyond my knowledge. Carolus would be the one to answer that.