That would likely combat the problem of people quitting the checkout process because they saw a coupon box and hunted for a code. However as a method of tracking referrals I'd expect its usefulness to be close to zero, as it ostensibly is still a coupon, and will appear on the websites that offer them as such.
People might voluntarily divulge who referred them to your store. Only with the correct entry do you get a discount, as an added bonus to people who answered.
So incorrect results arn't technically incorrect, they're just bonus data.
