My experience includes:
Orchestra librarians and their assistants perform an important function for any orchestra. The librarian must keep the orchestral parts for each instrument in the library, make sure they have all the necessary markings such as bowing for the strings etc. according to the specifications of the conductor, and make sure the parts are all in good shape and legible etc. The librarian must keep track of how many orchestral scores and parts in the orchestras library, must secure the score and parts for any orchestral works which are not in the library that the orchestra is scheduled to play, and take care of borrowing everything which any conductor may have chosen to perform. The librarian is a sort of liaison between the conductors and the orchestra members to make sure all the parts are ready for any given concert.