In-text author-date citation for range of years displaying incorrectly

Question

I have some entries in my bibliography with ranges of years for the date (sometimes multiple entries with the same author and date range). They are displaying correctly in the bibliography, but not in in-text author-date citations. I would like them to display as:

 (Author 1949, 1949-1950, 1950-1952a,b, 1950-2000)

(or something reasonable along those lines). Currently they are displaying as:

 (Author 1949,-, 1950-1952a,-,-)

I am using bibtex and natbib with this .bst file, and am not able to change any of these things now. The solutions in this post do not work for me.* I am guessing the problem is with the .bst file because when I was using a different bibliography style, it handled these differently.

*Update: either the hyphens or the slash will work in isolation e.g., (Author 1949-1950), but the same problem arises in a string of citations in one parenthetical.

Not exactly a MWE, but here are the relevant pieces and example bib entries.

@misc{bar1949a,
  author = {F. Bar},
  title = {Some title},
  year = {1949},
}
@misc{bar1949b,
  author = {F. Bar},
  title = {Some notes},
  year = {1949--1950},
}
@misc{bar1950a,
  author = {F. Bar},
  title = {Some more notes},
  year = {1950--1952},
}
@misc{bar1950b,
  author = {F. Bar},
  title = {Some recordings},
  year = {1950--1952},
}
@misc{bar1950c,
  author = {F. Bar},
  title = {A huge collection of notes},
  year = {1950--2000},
}

\documentclass{article}
\usepackage{natbib}
\bibpunct[:]{(}{)}{;}{a}{}{,}

\begin{document}
Blah blah blah \citep{bar1949a,bar1949b,bar1950a,bar1950b,bar1950c}. Blah blah blah.

\bibliographystyle{unified}
\bibliography{test}
\end{document}

Answer 1

I have found a manual workaround, thanks to the answer in this post.

\documentclass{article}
\usepackage{natbib}
\bibpunct[:]{(}{)}{;}{a}{}{,}

\begin{document}
Blah blah blah (\citealt{bar1949a}, \citealt{bar1949b}, \citealt{bar1950a}, \citealt{bar1950b}, \citealt{bar1950c}). Blah blah blah.

\bibliographystyle{unified}
\bibliography{test}
\end{document}

It would be even better if it just worked properly, though.