Why appearing both groups shall make no difference in attempt for Finals?
 If a student clears both groups in May 2010 he should be eligible in May 2012
ICAI has fixed firmly 6 months restriction ONLY for clearing Group 1. For registering Finals, obviously one requires to pass Group 2. So, accordingly:-
    
        
            | Cleared Group 1 in May 2010 | Register for article ship | 
        
            | Cleared Group 2 in Nov 2010 | Finals in Nov 2012 (last 6 months prior to May 2013) | 
        
            | Cleared both Groups in May 2010 | Register for article ship and Finals, Final due on???.  Nov 2012 (according to 6 months restriction) | 
    
There has to be some advantage offered to anyone clearing both groups.
A PCC student is well deserved to early attempt for Finals even if he clears PCC an year before Finals are due. In simple words a PCC student enjoys 3 attempts to clear whereas in IPCC you enjoy early articleship but Finals are delayed by 6 months (attempt after 2.5 yrs), even if you clear BOTH groups in first attempt!!