Hi Ron...hope you had good Xmas and New Year? Things must be quiet in the workshop if your talking about Velo gear changes ..LOL!
Based on my understanding...Velocette invented and patented the positive stop gear change in the 1920's but the original version was external to the gear box. You can see this on late 1920s cammy singles ( like my 1929 KSS) . They then in the mid 1930s internalised the positive stop mechanism on bikes like pre war MAC which became MDD and MAF models during the war. Having improved the system on their own bikes they licenced the old external deign to Scott to make some cash from the patent.
You can see above the mechanism is the round bit behind the gearlever attached to the top outside of the gearbox.If you look at pictures of Scotts you will see a similar arrangement.
With regard to chain and sprocket gear boxes I have seen articles in the classic bike mags with bikes that have these and they are usually one chain and a pair of sprockets per gear, the required gear sprockets engaged by dogs rather than a single chain and derailluer system.
Hope this helps.