Provisional assessment obligations: importers/exporters must provide requested documents so final assessment is completed within prescribed time. Amendment to section 18 inserts a reference to section 50 in sub section (1), adds sub section (1A) obliging an importer or exporter to submit documents or information requested by the proper officer for finalisation of a provisional assessment within the time and manner prescribed, and substitutes '28AB' with '28AA' in sub section (3), with that substitution given retrospective effect.