Leda may have started post 1952 as all the cards (in their many variations) reference the Federal Council of Drycleaners that was being proposed that year. The name Leda was trademarked by Beutron on 20th September 1957. Advertising from around 1958 feature ‘Leda buttons by Beauclaire’ and state that ‘Leda buttons are a product of General Plastics Ltd., Camperdown N.S.W’. Presumeably this indicates that General Plastics as a whole were by then owned by Beutron Australia Ltd. A line of Leda buttons continued to be marketed until at least 1966 (see the example below that has both pre and post decimal prices printed).
These were bought at Buttonfest 2016.