Comment by retorquere

> But in the Bibtex file it is very common for the titles to appear in their original title case form

That is common because they are following the rules about how to steer capitalisation when using bib(la)tex:

- If the entry is in English, and the style demands title case, output as is

- If the entry is in English, and the style demands sentence case, convert to sentence-case and output

- If the entry is not in English, output as is