There was an article about them on the BBC news site, to do with D Day. It stated that Chads originated in US shipyards during the later stages of the Vera Lynne War when, thanks to British money under Lend lease, the yards were stepping up production hugely for D Day. A lot of the work was rushed and shoddy, so an Inspector had to walk around all the vessels and mark them with chalk once he had passed them. The workers soon got their own pieces of chalk and made fake marks!
So, according to BBC, the Inspectors invented Chads to warn the workers that they were being watched.
So If Richard's Chad is definitely from 1929 this proves that it did not originate there and then, I suggest you contact the Beeb and put them right!