If we are talking about the same woman (only daughter but with several brothers, born late in her moms life), then she was alive and kicking when one of her siblings passed in 2020 (she is referred to as surviving sibling).
Yes Mostly Harmless was listed on his grandfather's obituary this year.
Maybe that was a mistake. This is a common pattern in UIDs, because they think said person is still alive, etc. (If you’re wondering why I’m on right now, I just have my students watching lessons I recorded. It really works well for them and follows the covid stuff)