Three-month filing period for reassessment returns; AO may grant extensions on application and late filings not deemed under section 139. A fixed filing period of three months from the end of the month in which the reassessment notice is issued is prescribed for returns under the reassessment provision, and the Assessing Officer may allow a further period on application by the assessee. Returns furnished beyond the period allowed are expressly declared not to be deemed returns under the primary return provision.