Each share in a company having a share capital shall be distinguished by its appropriate number:
Provided that, if at any time all the issued shares in a company, or all the issued shares therein of a particular class, are fully paid up and rank pari passu for all purposes, none of those shares need thereafter have a distinguishing number so long as it remains fully paid up and ranks pari passu for all purposes with all shares of the same class for the time being issued and fully paid up.