When the line you are looking at runs straight through the blind spot, you do not see a broken line. You see one continuous line. When the background is a texture, the texture appears to continue. This is called filling-in (or perceptual completion): the brain creates the missing part from the surroundings, so the hole stays invisible.

That means what you "see" at your blind spot is made up, not recorded. It is a very good guess most of the time, which is why nobody notices. It would be a bad guess if something small and different were hiding exactly there.