Biblatex-chicago notes sorting same year

Question

I'm sorry if this has already been answered elsewhere, but I couldn't find it. I would like to get Biblatex-chicago-notes to sort my bibliography when there are several works published the same year by the same author as in Biblatex-chicago-authordate, that is to say add a letter (a, b, c...) after the date/year field. I cannot find out how to do that, and it seems that it does it only in the authordate specification.

Here's a mwe:

\documentclass{scrbook}
\usepackage[notes,biber]{biblatex-chicago}
\bibliography{Bibliography}

% @book{Beck:2006pt,
%   Address = {London},
%   Author = {Ulrich Beck},
%   Publisher = {Polity},
%   Title = {Cosmopolitan Vision},
%   Year = {2006}}
%
% @book{Beck:2006kh,
%   Address = {London},
%   Author = {Ulrich Beck},
%   Publisher = {Polity},
%   Title = {Power in the Global Age: A New Global Political Economy},
%   Year = {2006}}

\begin{document}

Blablabla.\autocite{Beck:2006pt} And also blablabla.\autocite{Beck:2006kh}
\printbibliography
\end{document}

I get the result (never mind the ISBN, I'll add the ISBN=false option):

Answer 1

Since biblatex-chicago is specifically made to provide CMStyle, the code has to quite some lengths sometimes to comply with the CMS.

With that in mind, remember that you will probably violate the original CMS guidelines by doing this and remember that there might be corner-cases where the solution below does not yield satisfying results - there are quite some places where the style prints a date or year and I'm not entirely sure whether I snooped up all of them, also sometimes the style changes origdate and date which might lead to problems with the extrayear in these cases.

On with the modifications:

First we tell biblatex to provide us with the extrayear letters by adding the option labeldate at loading-time.

We then redefine two macros

\renewbibmacro*{cmsyear}{%
  \iftoggle{cms@switchdates}%
    {\printfield{origyear}}%
    {\printfield{year}\printfield{extrayear}}}

\renewbibmacro*{date}{% New for 0.9
  \iftoggle{cms@switchdates}%
    {\printorigdate}%
    {\printdateextra}}

In the first we added the \printfield{extrayear}, while in the second we replaced \printdate by \printdateextra.

MWE

\documentclass{article}
\usepackage[notes,backend=biber,labeldate]{biblatex-chicago}
\addbibresource{biblatex-examples.bib}

\renewbibmacro*{cmsyear}{%
  \iftoggle{cms@switchdates}%
    {\printfield{origyear}}%
    {\printfield{year}\printfield{extrayear}}}

\renewbibmacro*{date}{% New for 0.9
  \iftoggle{cms@switchdates}%
    {\printorigdate}%
    {\printdateextra}}

\begin{document}
Blablabla.\autocite{knuth:ct:b} And also blablabla.\autocite{knuth:ct:c}

Blablabla.\autocite{knuth:ct:b} And also blablabla.\autocite{knuth:ct:c}

\printbibliography
\end{document}