If in any legal proceeding for rectification of the register before the Appellate Board a decision is on contest given in favour of the registered proprietor of the trade mark on the issue as to the validity of the registration of the trade mark, the Appellate Board may grant a certificate to that effect, and if such a certificate is granted, then, in any subsequent legal proceeding in which the said validity comes into question the said proprietor on obtaining a final order or judgment in his favour affirming validity of the registration of the trade mark shall, unless the said final order or judgment for sufficient reason directs otherwise, be entitled to his full cost charges and expenses as between legal practitioner and client.