Keep in mind, it's also not uncommon for those in charge of others to have the same title. That is, in an engineering office the one in charge of a group of 1k engineers is likely an engineer as well, so they'd be a GS-14 or GS-15 electrical engineer. So the person who rose through the ranks of librarians from the lowest level to being in charge of a group of librarians would similarly be a GS-13 or GS-14 librarian.