Difference between notice under section 143(2) and 143(3)

My case got selected for scrutiny of IT returns.

ITO gave me notice on 14/08/2011 under section 143(2)  for my return submitted on 23/07/2009.

As I’m unable to attend on given date I send my friend(not a CA consultant).

When my friend met ITO he gave another paper with list of documents required to submit under section 143(3).

I have 2 question here.

1) Can ITO issue 143(2) notice for IT return submitted on 23/07/2009 after 2 years i.e notice date 14/08/2011

2) What is the reason for changing section 143(3) within a week when my friend met ITO with basic documents.

Thanks

Raju