54. On a consideration of the relevant sections as well as judicial precedent referred to above, what emerges is that, section 158BD of the Act deals with undisclosed income of a third party. However, in so far as the incriminating material of the searched person or other person detected during the course of search is concerned, the same can be considered during the course of assessment. Further, such incriminating material must relate to undisclosed income which would empower the Assessing Officer to upset or disturb a concluded assessment of the other person. Otherwise, a concluded assessment would be disturbed without there being any basis for doing so which is impermissible in law. Even in case of a searched person, the same reason would hold good as in case of any other person. As observed by us, detection or the existence of incriminating material is a must for disturbing the assessment already made and concluded. But, at the same time, such can be at three stages : one, at the stage when the reassessment is initiated, the second, at the stage during the course of reassessment and third, at a stage where the reassessment is altered by a different assessment in respect of searched person or in respect of third party. In this regard, reference may be made to the decision of the apex court in the case of Calcutta Knitwears (supra) and based on the said decision, the Central Board of Direct Taxes has also issued circular dated December 31, 2015, vide No. 24 of 2015.The relevant extract of the circular for ready reference can be extracted as under (see (2016) 380 ITR (St.) 32 ):
