Hervorhebung/Bezeichnung/Label für bestimmte Ereignisse in einer pgfplots-Darstellung

    \begin{filecontents*}{GDP.csv}
    Jahr,Total,Jung,Mittel,Alt
            1990-01-01,2.5,4.9,2.2,1.6
            1991-01-01,4.3,9.9,3.2,3.1
            1992-01-01,5.3,10.0,4.3,4.4
            1993-01-01,5.3,11.5,4.2,4.0
            1994-01-01,4.9,11.0,3.7,3.5
            1995-01-01,3.7,8.4,2.6,3.7
            1996-01-01,3.9,7.7,3.0,3.7
            1997-01-01,2.7,6.0,2.1,2.0
            1998-01-01,2.0,4.4,1.4,2.0
            1999-01-01,2.3,4.7,1.7,2.0
            2000-01-01,2.3,4.8,1.7,1.6
            2001-01-01,3.3,7.2,2.7,1.9
            2002-01-01,3.3,8.2,2.5,1.9
            2003-01-01,3.1,8.1,2.0,2.5
            2004-01-01,2.6,7.2,1.7,1.3
            2005-01-01,2.9,8.2,1.8,1.5
            2006-01-01,2.3,7.1,1.3,1.1
            2007-01-01,3.0,8.2,2.0,1.6
            2008-01-01,7.2,16.0,6.1,3.4
            2009-01-01,7.6,16.2,6.3,4.2
            2010-01-01,7.1,14.6,5.6,5.2
            2011-01-01,6.0,13.6,4.6,4.1
            2012-01-01,5.4,10.7,4.6,3.2
            2013-01-01,5.0,10.0,4.3,2.8
            2014-01-01,4.0,8.7,3.2,2.6
            2015-01-01,3.0,6.5,2.5,1.8
            2016-01-01,2.5,4.9,2.2,1.6        
    \end{filecontents*}
    \begin{filecontents*}{SPECIAL.csv}
    Jahr,Event
            1992-01-01,1
            1996-01-01,2
            2001-01-01,3
            2006-01-01,4
            2011-01-01,5
            2014-01-01,6
    \end{filecontents*}
    \documentclass[tikz]{standalone}
    \usepackage{pgfplots}
    \pgfplotsset{compat=1.15}
    \usetikzlibrary{plotmarks}
    \usepgfplotslibrary{dateplot}
    \usepackage[main=ngerman,icelandic,danish,frenchb]{babel}
    \usepackage[T1]{fontenc}
    \usepackage[utf8]{inputenc} 
     \usepackage[oldstyle,sflining]{libertine}
    \begin{document}

    \sffamily
    \begin{tikzpicture}
     %   \sffamily
          \begin{axis}[
          date ZERO=1990-01-01,
            date coordinates in=x,
            width=12cm,
            height=6cm,
            no marks,
            enlargelimits=false,
            xticklabel={\tiny\year},
               xticklabel style={rotate=45,anchor=north east},
          xtick={1990-01-01,1991-01-01,1992-01-01,1993-01-01,1994-01-01,1995-01-01,1996-01-01,1997-01-01,1998-01-01,1999-01-01,2000-01-01,2001-01-01,2002-01-01,2003-01-01,2004-01-01,2005-01-01,2006-01-01,2007-01-01,2008-01-01,2009-01-01,2010-01-01,2011-01-01,2012-01-01,2013-01-01,2014-01-01,2015-01-01,2016-01-01},
            xtick pos=left,
            xtick align=outside,
            cycle multi list={mark list\nextlist color list},
            ymin=-0,ymax=17,
            ytick={0,1,2,3,4,...,17},
            yticklabel={\tiny\pgfmathprintnumber[verbatim]{\tick}\%},
            ytick style={draw=none},
            yticklabel pos=right,
            ymajorgrids=true,
           legend style={
                    draw=none,
                    legend cell align=left,
                    at={(0,1.05)},% <-
                    anchor=south west,% <-
                    legend image code/.code={
                        \filldraw[##1] (-.5ex,-.5ex) rectangle (1ex,1ex);
                    },
                  },
                  legend columns=-1% <-
                  ]   
    \addplot table[col sep=comma,x=Jahr,y={Total}] {GDP.csv};
        \addlegendentry{Total};
         \addplot table[col sep=comma,x=Jahr,y={Jung}] {GDP.csv};
            \addlegendentry{16--24};
             \addplot table[col sep=comma,x=Jahr,y={Mittel}] {GDP.csv};
                \addlegendentry{25--54};
                 \addplot table[col sep=comma,x=Jahr,y={Alt}] {GDP.csv};
                    \addlegendentry{55-74};
   \addplot+[gray,ycomb, nodes near coords={\coordindex},
   nodes near coords style={circle,draw,inner sep=0pt,font=\sffamily}] 
   table[col sep=comma,x=Jahr,y expr={15.5}] {SPECIAL.csv};
        \end{axis}
        \end{tikzpicture}
    \end{document}