Game Club credits can be used with some sales, but free game codes from having filled a punch card cannot be used in this way.
The website says the following for this sale:
How do I use my Game Club credits for this promotion?
It’s easy!
Add the games you want to your cart and available credits will automatically apply to those games.
Type 2FOR1 into the “Have a coupon code?” box, then click Apply.
After applying the coupon code, one game will be free, and the other game will still have the Game Club credit discount.
However, free game codes that you get from filling punch cards are not applicable during sales.