Dear Friend,
In terms of Rule 11 of CER,2002, Assessee at any time can maintain only one set of invoice/invoice book.
However, an assessee can maintain Two sets of Invoice Books one for local sales and the other for Exports after intimating the same to the Jurisdictional Excise Division.
Further, the present Excise invoice being titled as Delivery Chalan cum Invoice, it can be used for charging VAT/CST also in addition to Excise duty.
Due to different trade practices, some assessees ( in a very rare cse from 1994 afet introduction of Invoice concept) may use Delivery chalan for the purposes of payment of duty and in such situations only commercial invoice being used for VAT/CST purposes.
Further, in addition to Excise invoices, there are other transactions also which a company generally dealt with. For instance, Scrap and other sales which does not involve Excise. In such situations commercial invoice is still being used. further, In case of some dealers who places orders on other dealers/manufacturers advising hte suppliers to consign the goods directly to the X party on his account. In such cases also commercial invoice is used. Though it is a private document , it have its own significance in the Financial transactions.
Best Regards
Suryanarayana