No, you don't need the 1099-R. You report an RMD as income in the year that you actually receive it, even if it's the RMD for an earlier year. On your 2025 tax return you will enter the 1099-R for the combined amount and pay tax on all of it on your 2025 tax return. That's an additional drawback of missing an RMD. You end up paying tax on two RMDs in one year.
The only purpose of the amended return is to add Form 5329. That form will show the amount you should have taken, but didn't, and request a waiver of the penalty. But it does not report the income. The amended return will not change your 2024 income or tax.
