i don't think there are 500,000 scjp certification. sun searched two or three month ago generally for the 500,000th certification. because of this and many people get first scea then scjp and more later i think there are less than 300,000 scjp certifications in the world. scea? perhaps not more than 50,000!
"Effective October 31, 2008, if you hold an exam voucher for this certification exam, you have through November 28th, 2008 to take the exam at an authorized Prometric worldwide testing center."
i think this is clear enough: you can only buy a voucher till 31.10 and the last day to take the exam is 28.11.08. when you think you need a retake and your exam`s day is after 31.10 but befor 28.11 then you should buy two... =)