I always notice this and it’s presence drives me mad. In all of the TVs I have owned, on the center of the sides of the viewing area there is an extra pixel of image that has it’s own column. It is always on both sides and in some cases I have noticed it at the top and bottom. What is the purpose of these superfluous pixels?
Are these TVs CRTs? If so, this is simply part of the design of an aperture grille display.
I think it indicates the center point of the height or width of the tube. Probably used for geometry adjustments.