In preparing the fifth edition of the Music Publishers' International ISMN Directory (MPIID), we focused even more on the reliability of published data, indispensible for any serious directory project. In addition to the information updates and supplements offered by the local and national ISMN agencies and other libraries and institutions able to deliver pertinent information to the editorial office, the International ISMN Agency undertook the task of contacting all 15,600 publishers directly. Publishers were asked to check their address data and to specify the areas of musical activity covered by their publications of printed music. In introducing such content criteria into the data survey, it is hoped that the efficiency of any attempt to retrieve data, with the help of one of the future editions of the MPIID, will be raised.