No, it is not okay to do that.
To do it right, you will need the last paystub from the state your client left. That should ideally tell you what the wages in that state were. Of course, reality sometimes gets in the way of ideally, as the client moves to a new state but payroll doesn't get the memo in a timely manner, etc. You will also need bank statements to determine interest income earned in each state, brokerage statements on the dividends and stock sales, and backup for your split of every number on the 1040. You can't just split those 50-50 either. And other items, like unemployment, may need special handling.
Keep in mind that some states, like NY, want the total wages reported in Box 16 even though that is not the actual NY wages. So it is possible that the totals in Box 16 on the W-2 will exceed Box 1. I am not sure what NC and CA require on that point.
