I am using DVD-R media. BEFORE I make a burn, there is a very small ring approximately 1 1/2 mm inside the burn zone. (Not sure about DVD architecture) AFTER I burn, I can look for that ring, if it is not visible, I get a good burn 99% of the time. If it is visible, the burn is always bad.
Don't know if this helps or if you know what I'm talking about. Maybe some guru's here can explain this better
But it has saved me frustration knowing that it IS a bad burn and not something else.