There has never been anything written regarding this. The ICAO requirement is that you must have demonstrated CPL level knowledge, but it doesn't say how. It is generally accepted that having passed the CPL written exams is a demonstration of CPL knowledge and it has always been accepted that those exams do not expire for the purpose of meeting the ICAO requirement for an FI course. For many years in the UK pre 1999 we simply had a pre-entry test which fulfilled that purpose.