Is this focusing on the NY state income tax return, or the federal income tax return?
I know next to nothing about NY state income taxes so if that's the focus here I'd suggest a new post explicitly mentioning the "New York" aspect of the question and clearing laying out the timeline of the events and alsomaking it clear that you're asking for help about your 2019 income tax return.
The whole issue of basis for securities inherited in community property or common law property states pertains to property passed between married couples. For federal tax purposes the basis of stock inherited by the surviving spouse does depend on whether they resided in a community property state or a common law property state, and how title was held. But at the death of the last surviving spouse the whole issue of community property/common law property state is irrelevant because the person(s) inheriting the securities isn't the spouse of the deceased. The basis of the stock in the hands of the deceased and how it was determined is no longer an issue because all the securities get a step up in basis at date of death.
The text quoted in my original reply makes this last point clearly: "The basis of property inherited from a decedent is generally...(t)he FMV of the property at the date of the individual's death." The section dealing with "Community Property" deals only with the special case of married couples inheriting securities from a deceased spouse.
I'd guess that most states follow the federal rules in this area, but that's a guess.
