Not sure about the dots.
Open levers were available from the 1940s through at least 1952, but the folded over levers were introduced together with the Mafac Racer centerpulls in 1952. I am under the impression that there was some overlap - the folded over levers were announced as a different model. But I can't say for sure. I saw a ca. 1955 or 55 A. Singer with folded over levers, which may indicate that the open ones weren't available any longer. Dots still were present on my 1962 A. Singer (with folded over levers, of course).
With so many bikes coming into this country in the 60s and 70s, we
should be able to determine when the dots disappeared.
--
Jan Heine, Seattle
Editor/Publisher
Vintage Bicycle Quarterly
http://www.mindspring.com/