Very interesting comments and infos, Marcello.
By: amanico : May 22nd, 2015-08:50
First, I never saw a 6542 underline, but why not, since there are some 6542 Exclamation Dot. Then, as for the period, I saw several " - " from 1960, several quartals. And now that you wrote it, some early 1964 ones... A few. When were the " - " 6542 dials...