Originally Posted by
irishguy28
Your sister didn't receive an upgrade, and therefore did not receive business class service (which is different from economy class, of course).
She was lucky enough to be seated in the business class cabin due to overbooking in Y (which happens fairly often on KLM - there are loads of threads about it on here), but she received economy class service. This should have been explained to her when she received her (new) boarding pass.
My daughter was never told that, and apparently this is common (from what someone else posted). In oversold situations on Delta she (and I) have been UPGRADED to business many times.