So you want to buy a lot that is part of an unregistered plan of subdivision? Here's another story about what can go wrong when a purchaser doesn't get legal advice prior to signing a contract...
Ryan signed a contract for a vacant block of land that was subject to an unregistered plan of subdivision. Ryan had noticed this in the contract and had asked the real estate agent about the unregistered nature of the block. Ryan was (wrongly) advised by the agent that the registration paperwork had been submitted to Land Victoria and would be back shortly, so he went ahead and signed the contract.
However, elsewhere in the contract, it said that the owner reserved the right to take 18 months to register the plan of subdivision and after Ryan signed, the seller indicated that they wanted to take all of that time. Ryan, who had organised to sell his current home to fund the purchase of the property, had to go through with that settlement and rent another a property for a year and a half before the plan of subdivision was registered and he could start building on the land.
Ask the agent for the contract and vendor's statement and submit it for review here BEFORE you sign!