Points can only be banked forward one year. Let's use an April Use Year as an example. The points you got on April 1, 2000 were banked. This means those points must be used between April 1, 2001 and March 31, 2002.
If points were "borrowed" into 2000, they have to be used between April 1, 2000 and March 31, 2001. Once borrowed or banked points can't be put back into their original year nor banked again.