In the 1960s and 1970s, Westinghouse larger tubes are dated in YQM format. Years in the sixties are represented by a travelling underline dash, and in the seventies by twice using a group of between 4 and 0 dots just below the top line of text. Bottom left is quarter represented by 4,3,2,1 dots in 60s and 3,2,1,0 dots in the 70s. Bottom right is month in quarter, represented by 2, 1 and 0 dots. Please view the attached pdf for details, or expand the photos.

I would like to thank everyone who helped solve the puzzle by providing outer case dates that were crucial in testing theories to eliminate rogue results.

Thanks for this, big help, I found it also works on some old westy MV lamps from the 60s.