I appreciate your thoughtful analysis (from two years ago), and completely agree with your reference to the importance of 'collective memory'.
A person very close to me spent her final few days disregarding tasks that would outlive her, while subtly reminding those close to her that she loved them, and tidying up the garden where she would end her life. She knew that this place would soon be filled with bereaved loved ones, which it indeed was. As the years pass since her death, at family gatherings I'm struck by the absence of her contribution to the collective memory. Everyone relating their personal recollection is being complete and honest, yet her perspectives of the story are forever missing. Crucial portions of an unfinished jig-saw image that can now only be guessed-at by those surviving contributing their parts.
In 'Stories We Tell', as in life, even if Diane Polley's contemporary voice were present, there would still be ambiguities. Memory seems to reinterpret our experience almost immediately, which underscores the value of the collective memory.
I applaud Sarah Polley for presenting this very personal story, and feel she did her courageous best with what remained of fading, individual perspectives while they were still accessible.
Soon you will be dead, and your name as but a vapor,
and all those who remember your name will also soon be dead.
(paraphrase of Marcus Aurelius)