What will happen if I submit identical SA100 twice?

Hi, I submitted SA100 (2023) with registered mail on 15 May 2023. From Royal mail track & trace, I can see it reached mailing centre on 20 May 2023 but still not deliver to the mail box (used to take just a few hours to deliver to mail box once it reached mailing centre). If I submit the SA100 (identical contents as the first one) again via courier, my question is - if Royal mail eventually deliver my first paper return, would HMRC simply ignore it as it has earlier date on it than the second copy? thanks

Hi wingsham,

If we process the 'second' return and then receive the first one, we would make no changes if the returns are identical.

Thank you.