Agree it's something they could/should fix, but they do provide an official solution- adding the membership ID card to one's digital wallet. If cast members are accepting the number in the
MDE app my guess is they're not following protocol since to your point the app is not able to prove whether or not you're eligible for membership benefits. I'd also consider the moral implications of getting the discount illegitimately. Yes it's on them to close loopholes but I personally wouldn't feel good about knowingly taking advantage of it.