Roll excess 529 contribution to another account

I just realized I contributed $100 more than the $18000 annual 529 contribution limit in 2024 to my son's account. I thought I could roll the extra to my own 529 account opened at the same brokerage firm. When I was on the phone with this brokerage firm, they told me they just roll the $100 to my own 529 but won't specify this is for 2024 contribution. Does that address my issue? I just worry if they don't specify the roll is for 2024 contribution, I might still exceed the contribution limit. Thanks!

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