The default citation styles verbose-trad1+; verbose-trad2 ; verbose-trad3 use the op. cit. form in order to have a shorter reference when a title has already been cited. However, when you cite two entries which share the same booktitle but not the same title, the op. cit. mechanism does not work. This package enables to obtain references like this: Author1, Title, in Booktitle, Location, Publisher, Year, pages xxx Author2, Title2, in Booktitle, op. cit, pages.