Q:

SAS: Reading Date field with one informat which it is saved in a different date format

I was trying to read a date field using date. informat from a SAS dataset. This dataset was created using a date format of mmddyy10. I thought I will get incorrect results when I realized that I was trying to read the date with incorrect format than what it was saved in the SAS dataset. 
Could someone clear me if it is a weird behaviour or SAS is intelligent to recognize that date. or mmddyy10. both represents the same date? 
DATA WORK.BOOKED_DEALER_TRANSACTIONS; 
  INFILE DEALER_RECORDS DSD; 
  INPUT @10 STATUS $15. 
        @26 TRANSACTION_REQ_DT MMDDYY10. 
        @ 46 PROCESS_DT MMDDYY10. 
        @63 DLR_NM $30. 
        @119 PROCESS_TIME TIME 
  ; 
  WHERE ORDER_STATUS = 'CONFIRMED_ORDERS';
run;

A:

Date values in SAS (when saved correctly) are stored as an integer, namely the integer number of days since 1/1/1960.  So today is 20230, for example.
Then formats tell SAS what it should look like when printed neatly; and informats tell SAS how to translate neatly printed dates to this number.  In your example, mmddyy10. is an informat which tells SAS to take 05/22/2015 and turn it into 20230.
You're welcome to then compare something with DATE9. format to this date value: because both will be stored as integers.  How they look on the screen is relevant to humans, but the integer is relevant to SAS.

