Sounds like the land equivalent of selling units off a plan.

Its most likely that they have DA approval but haven't registered with the LPI. Do you know if they went far enough to get a Subdivision Certificate off Council? I'd suggest contacting whichever the relevant Council is, talking to the duty planner and seeing what the status of the land is.

- What was approved;
- When was it approved;
- Has a subdivision certificate been issued;

Its possible that the subdivision is being registered in stages and the three lots left are the last stage (the lot numbers don't seem to suggest staging though), hence currently on the one title. Personally, I wouldn't buy until its registered so you are certain of the restrictions placed on the land and what the final dimensions are.