Why do IPI identifiers change?
Every effort is made to maintain stable IPI identifiers. When identifiers disappear from source databases attempts are made to propagate the corresponding IPI identifiers onto the IPI entries representing their successors. But often there is no clear successor for a disappeared entry, or two entries from one source database (each previously each represented by a separate IPI entry) are merged into a single entry (so one IPI identifier becomes redundant). A recent development has been the introduction of secondary ACs into IPI so that redundant IPI identifiers can be tracked to their successors. Click here for details. For a full description of how IPI identifiers are propagated, click here.
