(3) Where a design has been registered in respect of any article comprised in a class of article, the application of the proprietor of the design to register it in respect of some one or more other articles comprised in that class of articles shall not b refused, nor shall the registration thereof invalidated-
(a) on the ground of the design not being a new or original design, by reason only that it was so previously registered; or
(b) on the ground of the design having been previously published in India or in any other country, by reason only that it has been applied to article in respect of which it was previously registered: Provided that such subsequent registration shall not extend the period of copyright in the design beyond that arising from previous registration.