The default setting in MS Word will not display the ordinal for a date field when doing Mail Merge. To do this, following the steps below.
Procedures:
- Insert your date field twice. (SentDate is the field name in Excel)
- Highlight both field and click the right mouse button. Then choose Toggle Field Codes or press Alt+F9 
- Then change the content to { Mergefield SentDate \@ d \*ordinal } { Mergefield SentDate \@  MMMM, yyyy } 
- Then click the View Merged Data. 
- Now you can display the date format with ordinal. 
- From the menu bar click Tools -> AutoCorrect Options... 
- Then change to the Auto Format tab and clear all options except Ordinals(1st) with superscript, then click OK 
- Now, click Format -> AutoFormat... 
- Choose AutoFormat Now and click OK.  
- Now you can display the date format with ordinal in superscript format. 
 
                              