Citation call-outs for publications with same author, same year, and different titles

Question

When I cite publications that have the same author and the same year but have different titles, my TeX document appears to provide some citation like "blah blah (Institute, 2016c)" ... "blah bla (Institute, 2016a)." Even though I would assume it should provide to the first mention automatically the "a" behind the year. That is what I want but what ever I try do not get.

I use biblatex with options natbib=true, style=apa, and backend=biber.

\documentclass[fontsize=12pt,oneside,headsepline]{scrbook}
\usepackage[ngerman]{babel} 
\usepackage{blindtext} 
\usepackage{graphicx} 
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc} 
\usepackage{microtype}
\usepackage[onehalfspacing]{setspace} %h
\usepackage[urlcolor = black,plainpages=false,pdfpagelabels=true, 
    colorlinks=true,linkcolor=black,citecolor=black,
    bookmarksopen=true]{hyperref} 

\usepackage[style=apa,natbib=true,backend=biber,uniquename=false, 
   pagetracker=true,sortcites=true,sorting=nyt,backref=true,
   hyperref=true]{biblatex}

\DeclareLanguageMapping{german}{german-apa}
\DeclareFieldFormat{apacase}{#1} 
\DefineBibliographyStrings{ngerman}{ 
    andothers = {{et al\adddot}},  } 

\usepackage{parskip} 
\usepackage[german]{algorithm2e} 
\usepackage{tabularx} 
\usepackage{longtable} 
\usepackage{tablefootnote}
\usepackage{lmodern} 
\usepackage{subfigure} 
\usepackage{comment} 
\usepackage{placeins} 
\usepackage{scrpage2} 
\addbibresource{BeispielQVZ.bib} 
\usepackage{nccmath} 
\usepackage{tikz} 
\usepackage{amsthm} 
\newtheoremstyle{break}
    {8pt}{}%
    {\itshape}{}%
    {\bfseries}{}%  % Note that final punctuation is omitted.
    {\newline}{}
\theoremstyle{break}
\newtheorem{mydef}{Definition}[chapter]

\usepackage{tikz} % Für Zeichnungen mit dem tikz-Package

\usepackage{tablefootnote}

    \usepackage[all]{nowidow}
    \makeatletter
    \@removefromreset{footnote}{chapter}
    \@removefromreset{footnote}{part}
    \makeatother


    \begin{document} 

[...]

I am sorry, I have a very complex document already and I tried different options in the biblatex-line.

Can you please help me to achieve that the first appearance of an author is shown as "a", the second as "b", etc.? Of course, those letters behind the years should be shown in the bibliography at the end of the document, too.

Institute, 2016a, ...

I use \citep{institute2016somestuff} for citing.

Answer 1

If I understand your setup correctly, what you really want to achieve is to have biber sort the bibliographic entries only by authors' names and publication years, but not also according to publications' titles, right? By not sorting entries according to their title fields, they will de facto be sorted according to the ordering of the first occurrences of their respective citation call-outs in the body of they document.

Because your code sets the biblatex option sorting=nyt, all entries are sorted by their authors' names, then their publication year, and then their titles. To achieve sorting by only authors' names and publication years, simply define a new sorting option called, say, ny, via a \DeclareSortingScheme directive. There's no need to set the sortcites option to false, though.

Consider the following screenshot and code. There are 3 bib entries with the exact same author and year but with different title fields. (The entries keys are formed to incorporate information about their title fields.) In the body of the document, entry inst:16c is cited before entry inst:16a. If sorting=nyt were in effect, the entry with key inst:16c would be sorted after the entry with key inst:16a, and their year labels would be 2016c and 2016a, respectively. However, because sorting=ny is in effect, entry inst:16c has 2016a as its call-out label, whereas entry inst:16a has call-out label 2016c; in addition, entry inst:16c is listed before entry inst:16a in the bibliography. Put differently, the year labels in the citation call-outs and the sorting in the bibliography are now determined by the first occurrence of the citations rather than according to the alphabetical ordering of the respective title fields. (Of course, the entries with different years are still sorted by year, irrespective of the call-out ordering.)

Is this what you want?

\RequirePackage{filecontents}
\begin{filecontents}{mybib.bib} % create a dummy bib file with 5 entries
@misc{inst:15,  author="Institute", year=2015, title="zzz",}
@misc{inst:17,  author="Institute", year=2017, title="nnn",}
@misc{inst:16a, author="Institute", year=2016, title="aaa",}
@misc{inst:16b, author="Institute", year=2016, title="bbb",}
@misc{inst:16c, author="Institute", year=2016, title="ccc",}
\end{filecontents}

% I'm using 'scrarticl' instead of 'scrbook' so that output is all on a single page.
% I've also condensed the preamble to the bare minimum needed for this example.
\documentclass[fontsize=12pt,oneside,headsepline]{scrartcl}
\usepackage[ngerman]{babel} 
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc} 

\usepackage[style=apa, natbib=true, backend=biber,
   uniquename=false, pagetracker=true, sortcites=true,
   sorting=ny, backref=true, hyperref=true]{biblatex}

\addbibresource{mybib.bib}

\DeclareSortingScheme{ny}{ % see section 4.5.6 of the biblatex manual
  \sort{
    \field{presort}
  }
  \sort[final]{
    \field{sortkey}
  }
  \sort{
    \field{sortname}
    \field{author}
    \field{editor}
  }
  \sort{
    \field{sortyear}
    \field{year}
  }
}

\DeclareLanguageMapping{german}{german-apa}
\DeclareFieldFormat{apacase}{#1} 
\DefineBibliographyStrings{ngerman}{ 
    andothers = {{et~al\adddot}},  } 

% It's usually a good idea to load 'hyperref' last (with very few exceptions)
% Just for this example: set link color to 'red'
\usepackage[colorlinks=true,allcolors=red,plainpages=false, 
    pdfpagelabels=true,bookmarksopen=true]{hyperref} 

\begin{document} 
\citep{inst:16c,inst:16b,inst:16a,inst:17,inst:15}
\printbibliography
\end{document}