Wrong Posting Date

Hi All,
I am new to this Forum.
I would like to check the below issue. Our Finance user posted a credit memo on 19th April but the system captured as 11th April. There were 2 credit memos posted.
CN16-000070 – showing 19/04/16 which is correct.
CN16-000071 – showing 11/04/16 which is incorrect. This CN was posted after the CN16-000070. Have checked with the user whether she changed the date or not. She said NO. Would like to know what could have caused the issue.
Hope some one can help me.