PSA sat pax in the lower deck lounge of their Tristars in 1973 - it was cleared for pax there and had a under belly fairing fitted aft of the nose wheel in case of NG collapse etc
had a handy forward lower deck air stair too (court Line had a rear air stair fitted in aft hold that swung out for door 3R egress)
PSA only took delivery of only 2 of 5 built with lower deck lounges and LTU took the others i think - don't think LTU sat pax down there but they did use the lower deck lounge for a while?