Around the filing deadline each year, besides last-minute tax craziness, there are always questions about either late-filed or amended returns and whether or not a particular refund claim is timely.
We should not assume that a refund claim is time-barred simply because an original or amended return would be filed more than three years from the unextended due date for that tax year. The refund statute of limitations is complex, and it is quite possible that a refund claim filed many years after the unextended due date is timely.
https://www.tomtalkstaxes.com/p/preparing-and-submitting-irs-refund (May 2, 2025)