Interesting detail is that if you have 20 years of continuous service plus at least one day, then for purposes of the buyout you'd have 21 years and get 21 months, not 20, of pay.
Should correct this. The buyout is based on years of continuous service as of 11/30/2012. If you have a partial year it will count as a full year for purposes of determining years of continuous service. For example if your hire date anniversary is 10/31 and you have 15 years as of that day, the month of November will count as one more year so you'd have 16 years. One day of service beyond your hire date anniversary is enough to get one more year so if you were hired on 11/29 you are in luck, one extra year.