I believe that to be the case; if you held past the year the bonds matured you would need to amend.
Note that, from your original post, you have one year (2019) for which a timely return would have been filed in 2020 and the limitations period (again, for a timely filed return) would have expired in 2023. Also, the limitations period for the 2020 tax year will expire in just a few months (April, 2024) assuming you filed a timely return (in April of 2021). Just a note and not to say you shouldn't amend those returns.
