Indeed, a chord change could happen before or after the lyrics. In that case, there’s simply no corresponding underline.

Missing underline Meaning
Standard underline The first chord change of the line happens before starting to sing the lyrics
Dotted underline The lyrics of that line end before the second chord change

Take this one for instance:

C        G               Am      F
   Well, someone told me yesterday
C       G                   Am      F
   That when you throw your love away
C      G             Am               F
   You act as if you just don't care
C      G                 Am           F
   You look as if you're going somewhere

And its one-pager counterpart:

As you can notice:

  • there’s no solid underline on the first line of each pair of lyrics
  • the second line of the third pair of lyrics is also missing the dotted underline