"n.d.[a]" missing in bibliography

Question

Basically I am trying to implement this solution: https://tex.stackexchange.com/a/127158/17533 using this MWE:

\documentclass{scrartcl}
\usepackage[style=authoryear-ibid,backend=biber,dashed=false]{biblatex}
\DeclareLabeldate{\field{date}\field{eventdate} \field{origdate}\literal{nodate}}

\begin{filecontents}{\jobname.bib}
@online{Example,
  author = {Zuiop, Qwert},
  title = {TITLE 1},
  urldate = {2014-04-15}
}
@online{Example2,
  author = {Zuiop, Qwert},
  title = {TITLE 2},
  date={2012},
  urldate = {2013-04-15}
}
@online{Example3,
  author = {Zuiop, Qwert},
  title = {TITLE 3},
  urldate = {2013-04-15}
}
@online{Example4,
  author = {Zuiop, Qwert},
  title = {TITLE 4},
  date={2012},
  urldate = {2013-04-15}
}
\end{filecontents}
\addbibresource{\jobname.bib}
\addbibresource{sources.bib}

\begin{document}
Test\autocite{Example}
Test2\autocite{Example2}
Test3\autocite{Example3}
Test4\autocite{Example4}

\printbibliography

\end{document}

This results in:

However, the first two entries should contain "(n.d.[a])" / "(n.d.[b])", too:

Zuiop, Qwert (n.d.[a]). TITLE 1. (Visited on 04/15/2014).
Zuiop, Qwert (n.d.[b]). TITLE 3. (Visited on 04/15/2013).
Zuiop, Qwert (2012a). TITLE 2. (Visited on 04/15/2013).
Zuiop, Qwert (2012b). TITLE 4. (Visited on 04/15/2013).

How can I get this to work? I don't see any differences to the linked example which could cause this issue.