there are technically 12 emergency exits on a 747-400, 10 main deck and 2 upper deck. on the -400 fleet, all have always been armed and have slide packs fitted. the classic fleet of -100 and -200 aircraft were retired during 2002. some were sent to the mojave desert in arizona and some were sold to bea aviation and are still in active service. door 3 left and right were deactivated due to seat configuration. with less seats, less exits were legally needed and removal of two slide packs is a great weight saving I can tell you!
hope that helps