I'm not sure anyone here has tested it, but I believe as written only actual future year points are supposed to be borrowed back (which can be done within 90 days of check-in). That is, if I have 200,000 points next year and also deposited 100,000 points from this year to next year, I'm pretty sure only 200,000 can be borrowed (leaving 100,000 to be used next year). But I'm not sure if that's actually how the system works in practice.