I'll try to put this whole banking/borrowing thing together in one package, because it makes a lot more sense in the whole than it does when you look at a little question here and a little question there.
There are three underlying fundamentals with moving points from one use year to another.
The first is that, subject to some limitations and restrictions, you have the flexibility to move points from one use year to another. You can move them ahead one year and use them earlier (borrowing) or you can move them back one year and use them later (banking).
The second fundamental is that once you move points, you can't move them again. So borrowed points can't be "unborrowed" by returning them to their original use year, nor can they be saved for a future year by banking. Similarly, when you bank points to the next use year, you must use them or lose them during that use year.
The third underlying principle is that points expire at the end of the use year unless you bank them by the banking deadlines. That's the reason why, when you borrow points, you borrow only the exact number needed to complete a particular reservation - once you borrow them, you have to use them or lose them, so you don't borrow extra.
Banking - You can bank points to the next use year as many times as you want during the first nine months of the use year. You cannot bank points farther ahead than the next use year. Once you bank points, they are no longer available for the current year, but they are available for the entire next year. Your use year is February, so these are your banking deadlines.
By July 31 - up to 100% of your current use year points can be banked to the next year
By September 30 - up to 50% (remember that the banking is cumulative, so if you bank 20% of your points in March, you would only be able to bank an additional 30% of the annual points by September, for a total of 50%)
By October 31 - up to 25% cumulative
As mentioned above, banked points are either used or lost, so the points which you have banked now must be used by the end of Jan 06, or you lose them. If you're not going to use them, you should investigate renting/transferring the points.
Borrowing - Borrowing is more flexible than banking, and you should not lose any borrowed points unless you borrow and then cancel a reservation. You can borrow up to 100% of your next use year's points at any time during your current use year. You borrow only at the time of a reservation, and only to provide enough points to complete that reservation.
