If the family member booked the Getaway, why wasn't his/her name already on the reservation? If you booked the Getaway for them, I think the change in II practice is appropriate.
I booked it using my II account, but my BIL's credit card. II is fine with that, but I didn't get a guest certificate. I wasn't joining him on this trip and I was just trying to save him the extra $49.
However, in the past I've done this when I was traveling with friends. I often travel with friends and they sometimes arrive ahead of me. (I travel standby and often my friends will have a confirmed seat on the flight.) I've never had any trouble calling the Marriott resorts and telling them that my friends will be arriving ahead of me. I hate to pay for a guest certificate when I might arrive with my friends anyway.
A couple of years ago I booked an exchange into NCV and planned to vacation with some friends. My son had a medical emergency so I was delayed by a day. My friends arrived and checked in without any problems because I had called ahead and alerted the front desk.
I don't have a problem with this new policy of requiring a guest certificate. You are correct that this has always been II's policy, they want an extra $49 if someone else will be checking in.
I just wanted to alert others that NCV now requires a guest certificate if the individual on the confirmation isn't the one checking in. They no longer allow you to call and have them add another name.
Now I know what to expect when traveling to NCV with friends/family that might arrive ahead of me.