This is not just a NY-NJ problem, but is a complexity any time a taxpayer moves to a new state but continues to work in the old state. I’m not specifically familiar with the NY & NJ software, but this is how it’s handled in the states I am familiar with.
I assume you had $200K of total wages, not $270K. At the W-2 screen, on the line where NY is in box 15, you change the box 16 amount to $130K. Do not change the box 17 amount. Box 16 of the line where NJ is in box 15, should be $70K. Alternatively, you leave the NY amount as $200K and change the NJ amount to 0 (or deleted the NJ line).
You file a part year resident return for both states. You are going to have to allocate $70K of wages to NJ on the NJ return, but allocate the full $200 to NY on the NY return. So, yes $70K is the double taxed amount.
