if i'm not wrong, ghost notes are usually denoted similar to say ::
-(16)-17-
where u kinda "slide" very quickly from 16 to 17, giving the "impression" that 16 was played just b4 17. maybe for description's sake 16 = 1/4 second, 17 = full second, kinda thing. its sometimes noticeable, adds colour to the playing. let ring on the other hand is to hit the string and hold, again if im not wrong.