If a person has worked through Dec, then W2 is good to have; else it is not applicable. In other words, if you started working on H-1 in April 2012 and wife appears for stamping in Dec 2012, then 3-4 payslips are good enough and no W2 is required. However, if she appears for stamping in Feb 2013, then payslips and W2 for 2012 should be carried.