Rules relating to language of invoice

Sir,

One Maharshtra based manufacturing  company  ( on border of Gujarat) has issued invoices from 1967 to 1980.

1. Invoice is printed on letter head. Letterhead contents are in Marathi, but in particular caulamn of invoice, all contents are written in Gujarati.  Invoices have been issued in Maharashtra to local retailers. 
2. Invoice issuing company has produced those invoices in court of Gujarat in trademark case to prove the use of trademark. 

Are such invoices valid as per invoicing rules in India/ maharashtra?

Thanking you inanticipation