Those numbers can go up to 9; What J5 D4 means Qantas are prepared to sell up to 5 more J seats on the aircraft and four of those can go for discounted (D) business class. Given it's a 73H with 12 Millennium seats it's likely to be about 60% booked in Business Class at the moment.

Keep an eye on it; the longer D holds up the better your chances.