IRS has a notice for that, when it receives a paper return.  **bleep** between Social Security reporting and IRS processing.  The IRS instructions are good advice if the person is still alive, but I wouldn't expect too much interaction between the two agencies when it's only a matter of figuring out the right year.  You can put lots of time and effort into it, or you can file a paper return with a copy of the death certificate attached.

"We issue a CP01H notice when the IRS receives a tax return that contains a Social Security number (SSN) for an account that we locked because our records indicate the TIN belongs to an individual who died prior to the tax year of the return submitted.

The IRS locked your account because the Social Security Administration informed us that the Social Security number (SSN) of the primary or secondary taxpayer on the return belongs to someone who died prior to the tax year of the return submitted for processing."

https://www.irs.gov/individuals/understanding-your-cp01h-notice