More grist for the mill:
Here is the full text of New York's law regarding New York source income of a non-resident:
https://codes.findlaw.com/ny/tax-law/tax-sect-631.html
As far as I can tell, the only provision that would exempt a portion of the severance income from NY taxation has to do with former employees whose work was carried out partially within and partially without the state of New York (section (c)).
Also see this New York tax memo: https://www.tax.ny.gov/pdf/memos/multitax/m18_2c_3i.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
