Under the law in the case of a merger situation if a notice is issued to an erstwhile company, the subsequent company which has taken over the company is made liable to taxes u/s 170.
In  438 ITR 680 (Mad) the High Court went on to distinguish SC decision in PR. CIT v. MARUTI SUZUKI INDIA LTD.  416 ITR 613 (SC) where notice was issued u/s 148 in the name of non existent entity that had subsequently merged and the Apex Court held the proceedings void ab initio.
Vedanta case herein before the Madras High Court pertained to merger among companies within the same group and the department alleged thatthere being no change in the permanent account number, it is to be construed that the notice was issued to the person to whom it was intended to be issued i.e. the successor company .
The High Court at the same time held that if the notice was communicated to an unknown person, who is alien to the assessee, the benefit of section 292B cannot be given to the Department.
Interestingly Maruti Suzuki case also involved merger among known entities yet the Apex Court held otherwise taking a tight position under the law and undo the reopening processes undertaken already.