18.6. The commission may, on its own initiative or on an application, review or cancel any decision or order it has made and in respect of which no proceeding has been brought before the Administrative Tribunal of Québec(a) where a new fact is discovered which, had it been known in due time, might have justified a different decision;
(b) where an applicant or interested person was unable, for reasons deemed satisfactory, to present observations;
(c) where a substantial or procedural defect is likely to invalidate the decision or order.