César Vallejo wrote poems over a lifetime, but most was published posthumously.
He was not a musician; perhaps some of his poems were set to music by others; if so, copyrights for the musical works are determined by when it was composed.

Osip Mandelstam also was a poet. His "Earthly Life" was set to music by Elena Firsova in 1986 and broadcast by the BBC. Other works were set, including one in 1994, again by Firsova.
She and her publisher, Boosey & Hawkes, as well as the BBC, could hold copyrights on the musical works. Only declaimers of his poetry are home free. Musicians please pay.

As I said before, perhaps only the hog in Hogmanay may be served up for dinner. 0 out of 5.