The expiry date was never made clear. If I had to guess, they would expire at the end of the 2nd calendar year. As Embarc members, we had to plan to carry-over our points to a 2nd year by September 1st. "Bonus points" were given as incentives when buying additional regular points. But, they were just added to the year's allotment. There was nothing special about them. Bonus points seem to be a HGVC thing.
HGVC made our membership very complicated. Our Embarc year started on April 1st. All of our vacations were ski holidays and completed between January and March. So we were traveling on last years points, as it were. When HGVC wanted all member's years to be aligned with calendar years, we got screwed over. We had to use two years worth of points in one year.