there is block A, B, C, D and E.
when they opened for booking with the voucher first round, people was allowed to book block C, D, E. At that point they already mentioned block A and B not launching yet.
then a week before the launch they said block D will also be sold upon completion! means holding up 3 blocks.

probably to create the hype of 2 blocks sold out yadda yadda then they can increase price of the remaining 3 blocks~