I'd phone the resort and ask them. Be sure to get the person's name you talk to &/or get them to e-mail you their answer (for proof if needed). I've given family members with the same surname as ours Extra Vacation & Last Call weeks many times. Each time I called the resort to ask if a Guest Certificate was needed & each time the answer was no. I also gave family member a letter saying they had my permission to use my week & signed it including my home adr & tel #. Never had a problem. YMMV
~Diane