A swan song is today generally meant as a farewell act (before retirement or death) and is based on a very old legend in which the swan is through life mute but before death sings a very beautiful song.
From phrases.org.uk: The legend was known to be false as early as the days of ancient Rome, when Pliny the Elder refuted it in Natural History, AD 77:
"Observation shows that the story that the dying swan sings is false."
It is a poetic notion that has proven useful for many years. Chaucer used it, as did Shakespeare.
Samuel Taylor Coleridge (aside: I loved The Rime of the Ancient Mariner from my first encounter as a teenager) also used the concept in his poem On A Volunteer Singer:
"Swans sing before they die; ’twere no bad thing
Did certain persons die before they sing."
Nonetheless....a person gathers their life stories and some are shared and some are kept close but if a person has lived at a certain point there is a swan song. Even if it is seemingly silent.