You cannot use someone else's MR#, even a spouse, if that person isn't staying with you. If you lie and claim the spouse is going to be there, you are telling a lie to get certs you wouldn't otherwise get.

There is no problem if a couple travels together and alternates whose account is used. There is a problem if you intentionally deceive Marriott, and, according to Marriott, violate the T&Cs (asked the question, posted Marriott's answer in the other thread) in order to get certs that, if the truth were known, you wouldn't be given.

Otherwise, why don't we all just use other people's MR#s and get certs for every two stays? Marriott limits those who get certs to two certs per promotion. I'm getting 55k points for 25 stays. Why shouldn't I switch promos and get a dozen certs instead? Then transfer the certs to points and move them all to my account. Instead of 55k points, I can get 250k points that way.