You can transfer only "current" use year points, not any that have already been banked or borrowed. You can bank points that have been transfered to you but you cannot borrow them.
Borrowing is what you do when making a reservaiton and you do not have enough current use year or already banked points to cover the reservation. You borrow from the next use year to complete the reservation. There is no charge for borrowing and its only penalty is that once borrowed, the points can never be sent back to their original use year but must be used by end of use year into which they were borrowed.