See not two ppl can ever be of same face until or unless they r twins. If Thapki could convince teh whole world that she was Vaani and not Thapki then y can't the CVs show us that Aaryan n Bihaan had similar faces but they r not same. Also after 15 years there is no way Bihaan can look wat he looked like 15 years ago.
So we must accept that serials have nthg to do with logic but pure non sense