Folks,
The history of Smith and Sons Ltd. (England) can be found here.
http://www.smiths-clocks.co.uk/sm-orign.htm
This does not speak to the reverse action speedo's but it does give an accurate bit of information on the company.
My guess is that the story about not wanting to use the angle box in order to save money is the most likely one.
It is cheap to change a silk screen as compared to a gearbox fitment.