(2) Where an assessment is reopened under section 147, the assessee may, if he has not impugned any part of the original assessment order for that year either under sections 246 to 248 or under section 264, claim that the proceedings under section 147 shall be dropped on his showing that he had been assessed on an amount or to a sum not lower than what he would be rightly liable for even if the income alleged to have escaped assessment had been taken into account, or the assessment or computation had been properly made :

Provided that in so doing he shall not be entitled to reopen matters concluded by an order under section 154, 155, 260, 262, or 263.