Ich weiß nicht, wofür Du `uniquelist=minyear`. Jedenfalls erhältst Du das gewünschte, wenn Du nach *nach Auswahl des Stils Stils* `uniquelist=false` setzt. Das hält übrigens auch [Deine Anforderungen aus der verlinkten Frage][1] ein:
![alt text][2]
\documentclass[a4paper,12pt,oneside]{report}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman,english]{babel}
\usepackage[
backend = biber,
bibencoding = auto,
natbib = true,
sorting = nyt,
sortlocale = auto,
useauthor = true,
% uniquelist = minyear,
% uniquename = false,
style = authoryear,
uniquelist = false,
maxbibnames = 25,
minbibnames = 25,
maxcitenames = 2,
mincitenames = 1
]{biblatex}
\addbibresource{\jobname.bib}
\ExecuteBibliographyOptions{maxcitenames=2,mincitenames=1}
\renewcommand*{\mkbibnamelast}[1]{\textsc{#1}}
\renewcommand{\finalnamedelim}{ \& }
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@Article{Thomasetal2006b,
Title = {Title},
Author = {Thomas, R. and Webster, J.D. and Rhede, D. and Siefert, W. and Förster, H.J. and Heinrich, W. and Davidson, P.},
Journal = {L},
Year = {2006},
Number = {1--4},
Pages = {137--149},
Volume = {91},
Owner = {Unidentified},
Timestamp = {2015.04.27}
}
@InCollection{Thomasetal2006a,
Title = {Title 2},
Author = {Thomas, R. and Webster, J.D. and Davidson, P.},
Booktitle = {a book},
Publisher = {a publisher},
Year = {2006},
Editor = {Webster, J.D.},
Pages = {189--210},
Series = {Notes},
Volume = {36},
Owner = {Unidentified},
Timestamp = {2015.04.27}
}
@Article{VekslerThomas2002,
Title = {Title},
Author = {Veksler, I.V. and Thomas, R.},
Journal = {journal},
Year = {2002},
Number = {6},
Pages = {673--683},
Volume = {143},
Owner = {Unidentified},
Timestamp = {2015.04.27}
}
@Article{Meieretal2012,
Title = {Tilte1},
Author = {Meier, K.L. and Schulz, A.U. and Name, W.B. and anothername, E.E.},
Journal = {Journal1},
Year = {2012},
Number = {12},
Pages = {1777--1791},
Volume = {38},
Timestamp = {2015.04.27}
}
@Article{Meieretal1997,
Title = {Title2},
Author = {Meier, K.L. and Muller, A.U. and Schulz, W.B. and Name, E.E.},
Journal = {Journal2},
Year = {1997},
Number = {12},
Pages = {1777--1791},
Volume = {38},
Timestamp = {2015.04.27}
}
@Article{MeierSchulz1989,
Title = {Title3},
Author = {Meier, K.L. and Schulz, A.U.},
Journal = {Journal},
Year = {1989},
Number = {12},
Pages = {1777--1791},
Volume = {38},
Timestamp = {2015.04.27}
}
\end{filecontents*}
\begin{document}
bla \citet{Thomasetal2006a} bla \citet{Thomasetal2006b} bla
\citet{VekslerThomas2002} bla
Es sollte da stehen: bla Thomas et. al (2006a) bla Thomas et al. (2006b) bla
Veksler \& Thomas (2002)
bla \citet{Meieretal1997} bla \citet{Meieretal2012} bla \citet{MeierSchulz1989} bla
\printbibliography
\end{document}
[1]: http://texwelt.de/wissen/fragen/12997/biblatex-nur-erst-author-mit-et-al-im-text
[2]: http://texwelt.de/wissen/upfiles/biblatex_4.png