This patent, from 1945, shows the final incarnation of the TriVelox A1 derailleur system, with its sliding cassette and straight chainline. Before the Second World War the toggle chain that operated the system entered the hub axle from the left-hand, non-chain, side. After 1945 the design was improved so that the toggle chain entered through the right-hand, chain, side.
Reversing the operation had the advantage that the system became 'top normal'. The balance of the springs in the hub changed from big cogs to smaller ones - the easy, low power, change. The human rider, using the lever to pull the cable, did the harder work of changing from the smaller cogs to the larger ones. My rule for rear derailleurs is to always go for top-normal!
Another noteworthy aspect of this patent, is that there is no mention of the Triumph company. Alec Shuttleworth seems to have parted company with Triumph and to have teamed up with Smart & Brown (Engineers) Ltd.