So I have read that some may have lost your login discount coupons. Over the last couple of days, I have asked around. One real life friend of mine has also lost his 75% discount coupon when he wanted to buy the $200 G package. In his case, it was because his Steam Overlay was not enabled. The game produced an error and then the coupon was lost.
This could be one of the few reasons why a coupon is lost. I thought I share his experience with you in case yours is also disabled.
Cheers.