Admission of additional evidence: exceptions and safeguards require written reasons and opportunity for the assessing officer to rebut. Rule 46A limits admission of additional evidence before the Joint Commissioner (Appeals) or Commissioner (Appeals) to certain exceptions where evidence was wrongly refused by the Assessing Officer, where the appellant was prevented by sufficient cause from producing relevant evidence, or where the Assessing Officer denied opportunity to adduce evidence. Admission requires the appellate authority to record written reasons, and the Assessing Officer must be allowed a reasonable opportunity to examine, cross examine, or rebut the additional evidence. The appellate authority may also direct production of documents or witnesses where necessary.