como adicionar o ponto (.) antes do ano no arquivo chicago.bst?

Question

como adicionar o ponto (.) antes do ano (2012) no arquivo chicago.bst como abaixo

Bergmann, H. e U. Stephan, (2012). Passando do empreendedorismo nascente: medindo as diferenças transnacionais na transição para uma nova propriedade empresarial. Economia de Pequenas Empresas 41:945-959.

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eu adicionei a entrada BIB abaixo

@article{bs12,
author = {Bergmann, H. and U. Stephan},
title = {Moving on from nascent entrepreneurship: measuring cross-national 
         differences in the transition to new business ownership},
journal = {Small Business Economics},
volume = {41},
year = {2012},
pages = {945-959},
}

@article{bs12,
author = {Bergmann, H. and U. Stephan},
title = {Moving on from nascent entrepreneurship: measuring cross-national differences in the transition to new business ownership},
journal = {Small Business Economics},
volume = {41},
year = {2012},
pages = {945-959},
}

@ARTICLE{bgk10,
author = {Brinckmann, J. and D. Grichnik and D. Kapsa},
title = {Should entrepreneurs plan or just storm the castle? {A} meta-analysis on contextual factors impacrting the business planning-performance relationship in small firms},
journal = {Journal of Business Venturing},
volume = {25},
year = {2010},
pages = {24-40},
}

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 \documentclass[openany]{now}
   \begin{document}

   \nocite{*}
   \bibliographystyle{chicago}
   \bibliography{sample-bib}
   \end{document}