Cite (e.g.) the year from a bib latex entry which is crossreferenced

Question

In the following MWE, I want to cite the year pertinent to the Butz:Ur bib entry. However, this is a child entry and the year is (as expected) defined in the parent.

I am trying to figure out how to set up the citation so that it will, where necessary, daisy-chain back to the parent to get the information (rather than look up the parent manually and change the code)?

\documentclass{memoir}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@mvproceedings{Renger:state,
annote={bibliography verified},
title = {State and Temple Economy in the Ancient Near East},
volumes={2},
langid = {german},
Location = {Leuven},
eventtitle={International conference organized by the Katholieke Universiteit Leuven},
eventdate={1978-04-10/1978-04-14},
Number = {5},
isbn={90-70192-03-9},
Publisher = {Departement Oriëntalistiek},
Series = {Orientalia Lovaniensia Analecta},
editor = {Edward Lipiński},
pagetotal={xv+780},
date={1979}}

@inproceedings{Butz:Ur,
annote={bibliography verified},
crossref={Renger:state},
Author = {Kilian Butz},
Shorttitle = {Ur in altbabylonischer Zeit},
Title = {Ur in altbabylonischer Zeit as Wirtschaftsfaktor},
pages={257--409},
volume={1}}
\end{filecontents}

\usepackage{polyglossia}
    \setdefaultlanguage[variant=british]{english}
    \setotherlanguage[]{french}
    \setotherlanguage[spelling=old]{german}
\usepackage[autostyle=true,english=british,german=quotes]{csquotes} 

% BIBLIOGRAPHY SET-UP. Use British English and Chicago style
\usepackage[%
    notes,compresspages,
    isbn=false,
    backref=true,
    backrefstyle=two,
    dateera=secular,
    block=space,
    autopunct=true,
    language=auto,
    autolang=langname,
    backend=biber,
    urlnotes=false,
    hyperref=true
    ]{biblatex-chicago}
    \addbibresource{\jobname.bib}


\begin{document}
\mainmatter
We want the year for Butz: \citeyear{Butz:Ur} which should be the same as \citeyear{Renger:state}.
\end{document}

As currently written, the attempt to pull the year from the child entry fails. Relevant output follows:

Answer 1

For some reason I can't explain biblatex-chicago explicitly disables the inheritance of dateparts from @mv... types to all other types with (the question marks are not mine)

\DeclareDataInheritance{mvbook,mvcollection,mvproceedings,mvreference}%
{*}{% ???
  \noinherit{year}
  \noinherit{month}
  \noinherit{day}
  \noinherit{endyear}
  \noinherit{endmonth}
  \noinherit{endday}
  \noinherit{origyear}
  \noinherit{origmonth}
  \noinherit{origday}
  \noinherit{origendyear}
  \noinherit{origendmonth}
  \noinherit{origendday}}

We can get @mvproceedings->@inproceedings back with

\DeclareDataInheritance{mvproceedings}{inproceedings}{
  \inherit{year}{year}
  \inherit{month}{month}
  \inherit{day}{day}
  \inherit{endyear}{endyear}
  \inherit{endmonth}{endmonth}
  \inherit{endday}{endday}
  \inherit{origyear}{origyear}
  \inherit{origmonth}{origmonth}
  \inherit{origday}{origday}
  \inherit{origendyear}{origendyear}
  \inherit{origendmonth}{origendmonth}
  \inherit{origendday}{origendday}}

You could also write \DeclareDataInheritance{mvbook,mvcollection,mvproceedings,mvreference}{*} to get everything back, or be more conservative with \DeclareDataInheritance{mvproceedings,mvbook,mvcollection,mvreference}{book,inbook,collection,incollection,inproceedings,reference,inreference}

\documentclass{memoir}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@mvproceedings{Renger:state,
annote={bibliography verified},
title = {State and Temple Economy in the Ancient Near East},
volumes={2},
langid = {german},
Location = {Leuven},
eventtitle={International conference organized by the Katholieke Universiteit Leuven},
eventdate={1978-04-10/1978-04-14},
Number = {5},
isbn={90-70192-03-9},
Publisher = {Departement Oriëntalistiek},
Series = {Orientalia Lovaniensia Analecta},
editor = {Edward Lipiński},
pagetotal={xv+780},
date={1979}}

@inproceedings{Butz:Ur,
annote={bibliography verified},
crossref={Renger:state},
Author = {Kilian Butz},
Shorttitle = {Ur in altbabylonischer Zeit},
Title = {Ur in altbabylonischer Zeit as Wirtschaftsfaktor},
pages={257--409},
volume={1}}
\end{filecontents}

\usepackage{polyglossia}
    \setdefaultlanguage[variant=british]{english}
    \setotherlanguage[]{french}
    \setotherlanguage[spelling=old]{german}
\usepackage[autostyle=true,english=british,german=quotes]{csquotes} 

% BIBLIOGRAPHY SET-UP. Use British English and Chicago style
\usepackage[%
    notes,compresspages,
    isbn=false,
    backref=true,
    backrefstyle=two,
    dateera=secular,
    block=space,
    autopunct=true,
    language=auto,
    autolang=langname,
    backend=biber,
    urlnotes=false,
    hyperref=true
    ]{biblatex-chicago}
    \addbibresource{\jobname.bib}

\DeclareDataInheritance{mvproceedings}{inproceedings}{
  \inherit{year}{year}
  \inherit{month}{month}
  \inherit{day}{day}
  \inherit{endyear}{endyear}
  \inherit{endmonth}{endmonth}
  \inherit{endday}{endday}
  \inherit{origyear}{origyear}
  \inherit{origmonth}{origmonth}
  \inherit{origday}{origday}
  \inherit{origendyear}{origendyear}
  \inherit{origendmonth}{origendmonth}
  \inherit{origendday}{origendday}}

\begin{document}
\mainmatter
We want the year for Butz: \citeyear{Butz:Ur} which should be the same as \citeyear{Renger:state}.
\end{document}