I think it just depends upon the officer, who approves your case... If officer checks the expiration date of current document and if the expiration date of current document is in future (i.e., it is not expired yet) then officer may give the validity date from the next day of the current expiry date...
But I don't think that there is any rule regarding this.... also I don't think that any officer can approve case is a old (i.e., if you current documents were expired in past)....