With the following code:
\RequirePackage[
english,
ngerman]{babel}
\RequirePackage[
autostyle = true,
babel,
german = quotes]{csquotes}
\RequirePackage[
authordate,
bibencoding = auto,
strict,
backend = biber,
natbib
]{biblatex-chicago}
\DeclareCaseLangs*{german}
\bibliography{./_assets/bibliography.bib}
\defbibheading{head}{\chapter{Literaturverzeichnis}}
\AtBeginBibliography{\def\UrlFont{\scriptsize\tt}}
how do I get rid of the first part here before 2000?

biblatexis not set up correctly or if some auxiliary files are corrupted. Unfortunately, it is not possible to reproduce the issue with the information shared so far in the question. We would need to see a so-called MWE that starts with\documentclassand has a\begin{document}...\end{document}environment (see also https://tex.meta.stackexchange.com/q/228/35864, https://tex.meta.stackexchange.com/q/4407/35864). – moewe Mar 07 '19 at 05:29.aux,.bbl,.bcf, ...) and run the cycle LaTeX, Biber, LaTeX, LaTeX again. If the issue persists, please update the post with an MWE and include the.logfile of the last LaTeX run as well as the.blgfile (you can upload them to a text-sharing website such as https://pastebin.com/, https://0bin.net/, ... if they are too long for the question). – moewe Mar 07 '19 at 05:32\DeclareCaseLangs*{german}looks quite dangerous. It enables\MakeSentenceCase*for use with German. Which means that German titles will be subjected to English sentence case rules: The very first character is capitalised all other words will be in lower case. That will seriously mess with mandatory capitalisation rules in German and is therefore to be avoided. With\DeclareCaseLangs*{german}title = {Ein kurzer Titel},will come out incorrectly as Ein kurzer titel. – moewe Mar 07 '19 at 10:57