[old_tv_nut]

I believe gun placement would be simply a pass/fail, and only screen blemishes were considered for grading. Some C grade or similar tubes were sold as bench substitutes, so that only the chassis had to be brought into the shop instead of an entire set. Edit: I seem to recall in some cases the faceplate for bench subs was etched with "reject" to prevent service shops from buying them for resale.

Regarding adding more cathode material for longer life, it's not that simple, as (I thnk) the degradation would be to the surface and having a much deeper coating wouldn't help. Also, I don't know how changing the thickness would actually affect performance. More is not always better.

Much of the life is determined by internal cleanliness and achievement of a persistently good vacuum.