SP has a systematic process for changing identifiers. Changes are rare. The only situation encountered to date involves the replacement of an article with a new version of the same article at the Provider's request. The new copy of an article will supersede the old and claim the original identifier. The old copy of the article will retain the original identifier with “_old1” appended to the end. In the case of subsequent replacements, the replaced article will be appended with "_old<X>", where <X> is the next available integer.
Digital Preservation Policy Librarian