Anecdotally, on FamilySearch I created a profile for my great-grandfather's youngest sister marked as not living, as all of my great-grandfather's siblings had died in their sixties or early seventies. I couldn't find any info on this sibling after age 11 and wondered if she had died young.
Later, on Ancestry, I ended up stumbling across a woman with a tree that included my great-grandfather's family. Long story short, she was the granddaughter of my great-grandfather's sister - and her still living grandmother had just celebrated her 100th birthday the previous month.
Her grandmother had stopped going by her first name, using her middle name instead, and she had married, etc. Not long after that my dad's cousin sent me a copy of my great-grandfather's obituary and his sister was listed as a survivor, under her married name, plain as day...
So anyways, yeah, some people live past 100, even in families that are mostly not long-lived, and you no what happens when you assume...