Franking validity for articleship.. please help me

I am posting this for second time. Nobody is helpng me on this topic.. please sir help me on this.. Sir i hav done my franking on 7th august 2015 and have startd my articleship from 24 august.. bt my principal will register me after 15 sept.. so will the form in which i hav done frankng on 7th august be valid? And which will b the date of startng of my arriclshp.?