STUMPERS L

Can you complete the following list? The first answer is NOT 04 / 40.

01 / 10
02 / 20
03 / 30
_ _ / _ _
_ _ / _ _
_ _ / _ _

(BIG) HINT:
It has to do with the calendar.

Answers:

10 / 01
11 / 11
12 /21

The answers are the dates when the day and month of the year are mirrored:

01 / 10 - Jan 10 
02 / 20 - Feb. 20
03 / 30 - Mar. 30
10 /  1 - Oct. 1
11 / 11  - Nov 11
12 / 21 - Dec 21

( There is no 04 / 40 - April 40)