Now I'm reminded of my grandmother, who had always gone by her middle name. I knew that people who were adults other than my mom and her siblings called my grandmother this particular name, but when I was in my late teens, my grandmother was in the hospital and my mom told me that if I sent a card to her at the hospital, I would need to address it to [first name] instead of the name that I knew she went by. I opted to mail to the house for my grandfather to take up if it got there before she was going to be discharged, so addressed it the way I was more familiar. The obit (many years after that) had first and middle names (and her maiden surname in parentheses, even though she'd been married for 59 years when she died).
These days, I know the hospital has a spot in the chart for "patient's preferred name" which would cover issues like people going by middle names or nicknames.