In cases 1 and 2, as mentioned above by rfc1394, I would beg to differ. The proper term in these cases would not be unreadable, but rather illegible, which is used when something is impossible to read because of actual physical conditions, such as handwriting or the condition of the material written upon.

I am unsure of whether this should also be applied to cases 5 and 6, but I think that the common usage leans more toward unreadable.