Thanks, everyone for your time and expertise in answering my question.
@dmertz, I did request a waiver per IRS instructions and did make the corrective distribution. So I assumed the amounts my dad paid in 2024 were to "catch up" on paying income tax on the RMD distribution, but now I realize this is likely the excise tax. We need to revisit the 5329 he filed -- after looking at it, I believe it was not filled out correctly, and maybe we can reduce the excise tax from 25 to 10 percent.
I have a meeting w/a CPA today to try to sort it out.
Thanks again, everyone; I appreciate your help in working through this.
