biblatex: omit date from specific citations

Question

I'm writing a thesis using biblatex with APA citation style, i.e. the citations show up in the text as "Lastname, 1997". Now, I'm also quoting technical standards which contain their publication date within the title, and are supposed to be cited as e.g.
"ISO 22476-2:2010-1"
without an added publication year. I can put the standard name/number into the author field, no problem. But so far I've only had the choice between adding the year, resulting in
"ISO 22476-2:2012-03, 2012";
or omitting the year in the .bib file, resulting in
"ISO 22476-2:2012-03, n.d.",
both of which are ugly. How can I turn off the year output for single bibliography items while keeping it around for others?

MWE (in German) as follows:

\documentclass[enabledeprecatedfontcommands,german,11pt,a4paper,twoside,openany,BCOR=8mm]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[natbib=true,style=authoryear,citestyle=apa]{biblatex}
\bibliography{thesis.bib}

\begin{document}
This is a quote from \cite{lastname1997}. The machine he used abides by the rules in \cite{DIN22476}.
\printbibliography
\end{document}

Here's the bib entries:

@Misc{DIN22476,
author = {{DIN EN ISO 22476-2:2012-03}},
title  = {Geotechnische Erkundung und Untersuchung - Felduntersuchungen - Teil 2: Rammsondierungen (ISO 22476-2:2005 + Amd 1:2011); Deutsche Fassung EN ISO 22476-2:2005 + A1:2011},
}

@Misc{lastname1997,
author      = {Firstname Lastname},
title       = {Relevant publication},
year        = {1997},
date        = {1997-10-28},
}

Answer 1

Citations of standards are not always easy. You could try

@misc{DIN22476,
  title     = {DIN EN ISO 22476-2:2012-03},
  shorthand = {DIN EN ISO 22476-2:2012-03},
  subtitle  = {Geotechnische Erkundung und Untersuchung - Felduntersuchungen - Teil 2: Rammsondierungen (ISO 22476-2:2005 + Amd 1:2011); Deutsche Fassung EN ISO 22476-2:2005 + A1:2011},
  year      = {2012},
}

Here the shorthand is used for citations.

MWE

\documentclass{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[natbib=true,style=authoryear]{biblatex}

\usepackage{filecontents} 
\begin{filecontents}{\jobname.bib}
@misc{DIN22476,
  title     = {DIN EN ISO 22476-2:2012-03},
  shorthand = {DIN EN ISO 22476-2:2012-03},
  subtitle  = {Geotechnische Erkundung und Untersuchung - Felduntersuchungen - Teil 2: Rammsondierungen (ISO 22476-2:2005 + Amd 1:2011); Deutsche Fassung EN ISO 22476-2:2005 + A1:2011},
  year      = {2012},
}

@misc{lastname1997,
  author = {Firstname Lastname},
  title  = {Relevant publication},
  date   = {1997-10-28},
}
\end{filecontents}

\addbibresource{\jobname.bib}

\begin{document}
This is a quote from \cite{lastname1997}. The machine he used abides by the rules in \cite{DIN22476}.

This is a quote from \cite{lastname1997}. The machine he used abides by the rules in \cite{DIN22476}.
\printbibliography
\end{document}