The SSPL was used for several years back in the late 90's but none of the resorts were ever filled using the list, so it was abandoned. The program is still in place and could be brought back if deemed necessary at any time.
Basically, members were able to make reservations 13 months before arrival (this was only used for December 24 - 31) and allowed members to use the list to even get reservations at non-Home resorts before owners at that resort. If MS contacted a member to use the list and they declined, they could stay on the list for an additional year and then had to start all over at the bottom of the list. A lottery was used for the Y2K period where those on the list were contacted based on their position in the lottery drawing. That was also the final year of the Limited Theme Park Admission Program incentive for early buyers at OKW - providing free LOS park passes for up to 1/2 the occupancy of their reservation (2 passes for Studios/1BRs, 4 passes for 2BRs and 6 passes for GVs).
Even using the lottery system, there were still reservations available at both OKW and BWV once the 11 month priority opened for reservations. The system has not been used since December,1999.