This is an area that definitely needs work.  The IRS should allow efile for any tax years up until date of death (which they should already get from SSA).  If the taxpayer died in 2024 there's no reason for them to reject a 2024 return.  They should absolutely reject a 2025 return.  And since amended returns get processed manually anyway, why not let the preparer enter the data into the IRS computer (via efile) so the IRS personnel don't have to (and risk keying in something for the wrong amount or on the wrong line).