Credit Card Year

1. The at https://fill.dev/form/credit-card-simple autofilled my original card and it gave the wrong MM/YYYY - I guess 01/2020 is coded as NULL.
2. I created a copy of the original card. (different bank name and no 'spare info' such as phone numbers.
3. The copy worked correctly.
4. I did notice that on the original card the month was recorded as 6 not 06.
   
5. Went back to the original, correcting the 6 to 06.
6. Closed reopened 1P the original card at the test site, MM/YY still didn't work.
7. The Dummy bank card worked on the https://www.tropicalharvestqld.com.au/cart site.
8. The original still does not.
9. I can move on with the "dummy" bank card.

I'm still puzzled.