I’m the original poster. I am not a tax accountant but this is what we ended up doing.
We reported the full income (foreign and US) of the part-time resident spouse in federal tax return. I called the NJ tax hotline and they told me for the NJ tax return, to file jointly but NOT to report the foreign income that part-time resident made before he was a resident.
It’s been a few years now but if I remember correctly, we filed the NJ return ourselves on the NJ tax website. It allowed us to upload any supporting documents. I included a letter explaining the situation and documenting the name of the person we spoke to on the phone who told us to exclude the foreign income.
Note that this is for foreign income. If you were a resident of another US state, then there’s probably a different path to follow.
