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I turned 73 in May, 2023.  My understanding is that I need to take an RMD for 2023 by April 1 of 2024.  Is that correct?

If my understanding above is correct - I took most of my RMD before 13-31-2024 but  I need to take a little more.  If I take this additional part of my RMD how will the custodian know it should count for 2023 instead of 2024?  The custodian's withdrawal process doesn't ask me to what year the RMD applies.  How do I handle that?