Amendment to succession certificate

I had obtained succession certificate in1990 for 298 shares held by my mother at the time of her death in 1977.Meanwhile,the company issued bonus shares(463 shares) in 1982 and 1986 increasing the total holding to 761 shares.We were not aware of the bonus issues as we had migrated.Only when I took up for transfer I came to know of the bonus shares .The company asked me to produce an amended certificate.There were protracted correspondence. In 2004,there was a demerger and new shares were issued in lieu of old shares and after that there are bonus shares also.The company wants me to get an amended certificate mentioning the new share details in the place of old 298 shares. When I approached a lawyer to amend, he told me that it cannot be done as it is more than 25 years old and court records may not be available. Besides amendment is not possible and advised me to file a fresh succession certificate. It will be difficult to file afresh as two of the legal heirs are passed away and to coordinate the remaining highly difficult as they had already got their share. Please guide me. I am prepared to pay your fees if any in this regard.