I can answer this authoritatively, since I don't run a blood bank and don't know the procedures. But I imagine a blood donor card might tell the Red Cross (or whomever), "Hey, good - it looks like we MIGHT have some Type O blood here". But I would considerer it totally irresponsible - and inconceivable - for them to go giving that blood to somebody else without typing it themselves. Not to mention testing if for hepatitus, HIV, etc. Same thinking goes for if you ended up in a hospital needing blood. I imagine they would type you before giving you anything, not matter what your card said you needed.

If things DON'T happen like this in real life, well, it's no blood for me! I'll take the Ringer's or NS, thank you. I certainly don't want any blood that went through the stringent quality control of "Oh well, we THOUGHT it was OK to give you this. Better luck in your next life. Sorry about that..."