Mail Merge dates to word

[smscheung]

When I am mail merging a column with dates to word, the format I am expecting is DD MM YYYY, however I don't know why some show 01 04 2021 (correct), but some show 05 20 2021 which the month and day is the wrong way round, the data come from the same column with same format, what went wrong? Thanks for your help.

 

[smscheung]

Nevermind, just foud out what happened, thanks.

 

[smscheung]

Nevermind, just foud out what happened, thanks.

Wait, although I changed the mail merge cell format in word to the correct DD MM YYYY, but when it comes to April 1st, it comes out the other way round. I have used this formula in my excel:
=IF(AP41<DATE(2021,4,1),DATE(2021,4,1),AP41)
Is there something wrong with this formula to cause the mail merge comes out the other way round?
Many thanks.