In biology classes at school I was taught that O can be a donor to all blood types (given matching Rh group and other details), and AB can receive transfusion from any type. Quick googling seems to suggest this is true, at least theoretically for example, Wikipedia
However, I recently came across a discussion thread (in Facebook) where more than one person (at least one of them went for internship as nurse) claims that this is only true in theory, in practice transfusion is only allowed for exact same blood type (e.g. AB can only receive from AB). And once in a while I receive chain message from friends saying something like "My relative is in emergency, need AB donor urgently" (or need A donor, or need B donor) despite they should be able to find O which is the most common blood type.*
Can I find an authoritative reference that mentions universal donor transfusion is regularly done without any problem, and the "universal donor" concept isn't just theoretical?
*All these discussions and chain messages happen in Indonesia.