They can offer it to anyone, but they can and should program the registration line to reject the unqualified.

A computer that can be programmed to say "Sorry, you've already registered" can just as easily be programmed to say "Sorry, you're not eligible to enroll."

The invitation reads "non-transferrable," but some took that to mean you can't share your rewards with others, not that only the invited need apply.

Finally, the cards didn't carry a member's SM number. Others in a household might plausibly think it was for the family, too.

DL has registered all comers..denied some, honored others and explained very little.