Did some additional research and apparently the trains were ordered by SABENA, which also owned the trains. NMBS/SNCB operated the trains on behalf of SABENA. When they were delivered they were numbered 851, 852, 853, 854, 855 and 856. Originally these trains had only first class on board. Later SABENA sold the trains to the NMBS/SNCB which renumbered the trains to 595, 596, 597, 598, 599 and 600. Today these trains are still operational, however they are repainted and feature a "new" interior.