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.

I noticed in the 1960’s date sheet towards the end it’s referenced that as in the 50’s, Westinghouse again in the 1970’s began using a subtracting dot date code system. I was curious if a 1950’s Westinghouse date code sheet existed? I’ve rarely seen any posted lamps dated with that etch style and have a few early 50’s Westinghouse lamps myself I’m not sure the date on. I’d appreciate any info into the date code system