Airlift for April 1963 had an article on airliner JATO. It said American, Ansett-ANA, Braniff, Caribair, Ethiopian, Pan Am, Panagra, TACA and Trans-Australia had tried it, tho maybe Pan Am never had it on scheduled flights. "there have been eight actual emergency Jato firings, three in scheduled airline service..."
It says AA used it on DC-4 freighters out of Mexico City in 1947; Braniff and Panagra used it at La Paz. Ansett-ANA and Trans-Australia added it to their DC-3s in 1961.
The original units were only allowed 100 hours on the aircraft; in 1955 CAA approved 500 hours or a year, whichever came first. "During the past year, storage life has been upped to four years and flight time 750 hours or 18 months."