Thought I'd add my rendition -

When the +notes are clustered together it inidcates that they should be blended as one note.

This means don't pause between blows, just drag the harmonica to the next note.

When the + and - notes are clustered, it indicates a very quick in-out-in movement.

+5+6     +6    +7-7+7    +7    -8        +7    -6    +6
A--a    ma   z-in-g    graaaace, how    sweet    the    sound

+5+6    +6           +7-7+7    +7          +8+9   +9
Th-at    saved        a-a-a      wretch    li-ke    me

+7+8     +9      +8-8+8     +8        -8     +7       -6    +6
I-I        once    w-a-s      lost,    but    now    am    found

+5+6    +6         +7-7+7    +7    -7    +7
Wa-as    blind    b-u-t       now   I    see