Always print the final author name in bibliography

Question

I try to set up a bibliography style for a journal which has a pretty tricky requirement:

For references with up to eleven authors, all authors are listed. If there are twelve or more authors, only the first nine and the last one are listed, while the others are replaced by "(...) &".

For example:

Blackburn, T.M., Essl, F., Evans, T., Hulme, P.E., Jeschke, J.M., Kühn, I., Kumschick, S., Marková, Z., Mrugała, A., (...) & Bacher, S. 2014. A unified classification of alien species based on the magnitude of their environmental impacts. PLoS Biology 12: e1001850.

It means that in the bst file, I have to:

• Replace "et al." by "(...) &" which I am able to do thanks to the community

• Make the final author name follow "(...) &". This task is not straightforward for me.

I have already explored the possibilities offered by custombib but I have not found what I am looking for.

Answer 1

Original solutions

Thanks to @moewe, I have finally got what I wanted:

1. Always print the last author in bibliography
2. Replace "And" by the ampersand ("&") both in text and bibliography

Minimal Working Example

Here is the minimal working example that I have found in the solution linked by @moewe:

\documentclass[american]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authoryear-comp, 
    backend=biber, 
    maxcitenames=3,
    maxbibnames=999, 
    %Remove given names in in-text citations:
    %https://tex.stackexchange.com/questions/65747/citation-style-in-biblatex-1-get-rid-of-first-names-2-remove-comma-before
    uniquename=false,
    uniquelist=false,
    %Print only first initials in bibliography:
    %https://tex.stackexchange.com/questions/21974/biblatex-abbreviated-author-names?rq=1
    giveninits=true,
    natbib = true]{biblatex}

%------------------------------------------------------------------------------
% Set up a bibfile example

\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@book{legendre,
    series = {Developments in {Environmental} {Modelling}},
    title = {Numerical {Ecology}},
    isbn = {978-0-444-53869-7},
    publisher = {Elsevier Science},
    author = {Legendre, P. and Legendre, L.F.J.},
    year = {2012}
}
@inproceedings{cheshkov,
  author    = {Cheshkov, S. and Tajima, T. and Chiu, C. and Breitling, F.},
  title     = {Emittance control in Laser Wakefield Accelerator},
  booktitle = {American Institute of Physics Conference Series},
  date      = {2001-05},
  volume    = {569},
  pages     = {163-176},
}
@article{dehant,
  author = {Veronique Dehant and Bruce Banerdt and Philippe Lognonné and
Matthias Grott and Sami Asmar and Jens Biele and Doris Breuer and François
Forget and Ralf Jaumann and Catherine Johnson and Martin Knapmeyer and
Benoit Langlais and Le Feuvre, Mathieu and David Mimoun and Antoine Mocquet and
Peter Read and Attilio Rivoldini and Oliver Romberg and Gerald Schubert and Sue
Smrekar and Tilman Spohn and Paolo Tortora and Stephan Ulamec and Susanne
Vennerstrøm},
  journal = {Planetary and Space Science},
  number  = {1},
  pages   = {123 - 145},
  title   = {Future {Mars} geophysical observatories for understanding its
internal structure, rotation, and evolution},
  volume  = {68},
  year    = {2012},
}
\end{filecontents*}

\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}
%------------------------------------------------------------------------------
%Replace "And" by the ampersand both in text and in bibliography 
%https://tex.stackexchange.com/questions/68053/use-ampersand-in-citations-and-bibliography-in-biblatex

\renewcommand*{\finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
    \addspace\&\space}

%------------------------------------------------------------------------------
% Make the final author name follow etint 
% https://tex.stackexchange.com/questions/377543/using-the-et-int-citation-system

\NewBibliographyString{etint}
\DefineBibliographyStrings{english}{etint = {(...)}}

\newcounter{bbx:etinttrunc}
%Number of authors before etint:
\setcounter{bbx:etinttrunc}{6} 
\newtoggle{bbx:showetint}
\DeclareNameFormat{given-family-etint}{%
  \ifnumequal{\value{listcount}}{1}
    {\toggletrue{bbx:showetint}}
    {}%
  \ifboolexpr{
    test {\ifnumless{\value{listcount}}{\value{bbx:etinttrunc}+1}}
    or test {\ifnumequal{\value{listcount}}{\value{liststop}}}
    or 
      ( test {\ifnumequal{\value{listcount}}{\value{bbx:etinttrunc}+1}}
        and test {\ifnumequal{\value{liststop}}{\value{bbx:etinttrunc}+2}})
    }
    {\ifgiveninits
       {\usebibmacro{name:given-family}
          {\namepartfamily}
          {\namepartgiveni}
          {\namepartprefix}
          {\namepartsuffix}}
        {\usebibmacro{name:given-family}
          {\namepartfamily}
          {\namepartgiven}
          {\namepartprefix}
          {\namepartsuffix}}}
    {\iftoggle{bbx:showetint}
       {\usebibmacro{name:delim}{\bibstring{etint}}%
        \bibstring{etint}%
        \togglefalse{bbx:showetint}}
       {}}%
  \usebibmacro{name:andothers}}

\DeclareNameAlias{sortname}{given-family-etint}
\DeclareNameAlias{author}{given-family-etint}
\DeclareNameAlias{editor}{given-family-etint}
\DeclareNameAlias{translator}{given-family-etint}

\begin{document}

\citep{legendre,cheshkov,dehant}
\printbibliography

\end{document}

The MWE gives: