returns

you can file return for F.Y 2008-09 before 31st march, 2011

For F.Y 2009-10 before 31st march, 2012

for the F.Y before 2008-09 there is no option you can't file ur return

if your client have  income less than exemption limit ,

then u can give them certificate, that their income was belove exemption limit bcoz of this they was not file their return.