区分 natbib 中的 et.al a. 和 et.al. b

Question

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{natbib}

\title{A}
\author{B}
\date{\today}

\begin{document}

\maketitle


\cite{jia2019efficient}
\cite{jia2019towards}


 \bibliographystyle{chicagoa}
 \bibliography{Composite_reference}

\end{document}

bib文件内容如下：

@article{jia2019efficient,
 title={Efficient task-specific data valuation for nearest neighbor algorithms},
  author={Jia, Ruoxi and Dao, David and Wang, Boxin and Hubis, Frances Ann and Gurel, 
  Nezihe Merve and Li, Bo and Zhang, Ce and Spanos, Costas J and Song, Dawn},
 journal={arXiv preprint arXiv:1908.08619},
  year={2019}
}


@inproceedings{jia2019towards,
 title={Towards efficient data valuation based on the shapley value},
  author={Jia, Ruoxi and Dao, David and Wang, Boxin and Hubis, Frances Ann and Hynes, 
Nick and G{\"u}rel, Nezihe Merve and Li, Bo and Zhang, Ce and Song, Dawn and Spanos, 
Costas J},
  booktitle={The 22nd International Conference on Artificial Intelligence and 
 Statistics},
  pages={1167--1176},
  year={2019},
  organization={PMLR}
}

但生成的文档并未区分这两个引用。