I have a relative who has an unfortunate condition that causes internal bleeding. They’ve had enough blood transfusions that their antibodies are completely haywire.

Multiple times, doctors have not listened to their protests, and given them O-. They turn an impressive shade of yellow (among other, more serious, issues).

Last I heard, there were 2 compatible donors known, 1 in a different country. Thankfully, you can store blood longer term. It’s just not cost efficient to do in bulk. They have their own little stockpile of blood at their local hospital (mostly self donated).