I have a tex file (taken from this answer)
\documentclass[reqno]{amsart}\usepackage{mathtools,hyperref}\hypersetup{ colorlinks=true, linkcolor=blue,}\usepackage[overload]{empheq}\begin{document}\section{Intro}\begin{subequations} \label{eq1} \begin{empheq}[left={\eqref{eq1} \quad \empheqlbrace}]{align} A & = B , \label{eq1:a} \\ C & = D . \label{eq1:b} \end{empheq}\end{subequations}System \eqref{eq1} contains the subequations \eqref{eq1:a} and \eqref{eq1:b}.\end{document}
The author uses \begin{empheq} ... \end{empheq} to be able to reference to sub-equations. The author uses the option left={\eqref{eq1} \quad \empheqlbrace} to manually insert numbering of the group.
Can we make the manually-inserted numbering \eqref{eq1} flushed to the left and the content of \begin{empheq} ... \end{empheq} centered?