You can use three years worth of points, but you can not bank more than one years worth of points.
For instance you have a 200 point contract.
You bank from Year A to Year B, giving you 400 points to use in year B.
Then in year B, you also borrow from year C, now giving you 600 points to use in year B. When year C comes around, you'll have no points.
Then repeat the process, banking year D to year E, borrowing from F to E for a 600 points reservation in year E and so on.