Um, actually, for the transliteration, no one really would have noticed. Now, if you want to go by the official rules, 'Koprivshtitsa' would have been right. But since no one actually cares so much about those rules, outside of the cases when translating official documents, anything between
Koprivshtitsa
Koprivshtica
Koprivstitsa
Koprivstica
would have been valid. Treatment of letters such as ж, ч, ц, ш, щ, ъ etc is pretty loose when it comes to transliteration into Roman letters, heh.