# How to write additional content into bbl file?

How can I tell LaTeX to write additional content to bbl file?

Background of my question (see also MWE below): The page number for the bibliography displayed in the table of contents is correct if and only if \addcontentsline{toc}{chapter}{Bibliography} is placed at the beginning of the thebibliography environment. Hence, using bibTeX I need to write \addcontentsline{toc}{chapter}{Bibliography} into the bbl file. If I place it before \begin{thebibliography} the page number is first page of bibliography - 1, if I place it after \end{thebibliography} it is last page of bibliography + 1 (which in the MWE would be correct but not in general).

\documentclass{book}

\begin{document}
\tableofcontents

\begin{thebibliography}{B}
\bibitem[B]{B}
A. Brown
\newblock {\em Mathematics}.
\end{thebibliography}

\end{document}
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