The only reason I can see to buy & attach supplemental vacation days during the bidding process...is if you want them in the 01DEC-10JAN carve-out period. That is pursuant to the vacation award. I wanted 4 days attached to the my 25NOV-08DEC vacation. Found out afterwards that it had to be 7 days. Now that my 2 weeks of primary vacation have been awarded...even though 09DEC-15DEC is still an available week, I cannot buy and attach days in December. If I had Secondary vacation, I could buy and attach them to that week, pursuant to the bid award.