The RH factor makes your blood type rare. Only about one in 15 people are O-. You should be thanking your stars you are not AB negative. It is the rarest blood type. Only one in 167 people are AB negative. I think they can store rare blood types for up to 10 years. Normally blood is only stored for 6 weeks and then it is disposed of. In my youth, a friend of mine was an entomology student. He used to get expired blood from blood banks and feed it to his (i.e. the university's) insects.