Rapido keeps the old ILL number (External ID) when a borrowing request is not filled and moves on to another partner. The Ext ID number should be unique between a pair of partners. Right now you can have a Rapido request with a RapidILL number, a British Library request with a RapidILL number etc. Because each partner type has a different set of conditions (ex. allowance of renewals), each time you have a different type of partner, there should be a new Ext ID number.