oh I get it now! according to what I found :
Note: You can only view the last queue number invited for selection for the area and the type of flat you have balloted for during that exercise and only if you have not selected a flat.
The line you see would read
“Last queue number invited for selection of a _____ (insert flat type) in _____ (insert flat area) under ____ (insert sale launch) as at _____ (today’s date).
For example, if you had balloted for a 3 room flat in Punggol under the May 2015 BTO, had been invited for a flat selection but have not yet selected your flat, you would see
“Last queue number invited for selection of a 3 room flat in Punggol under the May 2015 BTO as at 14th Dec is XXX.”
This queue number indicated is not reflected real-time but is updated on a daily basis and shows the last number which would have been invited that day.
so perhaps only when we received letter then able to see?