The adf serial website provides details on the RAAF VV aircraft:
Welcome to ADF Serials
You will need to select 'Second RAAF Series', then 'A27' to get access to details of all the RAAF VVs.
A27-99 (aka EZ999) is listed there, with its service history IAW Megan's above quote.
I believe it is indeed EZ999:
1. The serial number painted on it is not fictitious, as I am sure this aircraft's history is consistent with the RAAF E/E88 aircraft data card. Unfortunately I no longer hold a copy of this card (which has been summarised above) - I have given all my source material to the Research Centre at the nearby RAAF Amberley Heritage Centre.
2. These cards are official documents, and although sometimes contain errors, cannot be doctored to change 'one airframe into another'. If there are Mk.IV VV components, then I would argue this would be consistent with its post-Service role, of being a plaything for technical trainees at the Sydney Technical College through the 1950s and early 1960s. I imagine the Mk.Ia was quite unsophisticated and empty by the time it was struck off charge and given to the Tech College, so a multitude of goodies were added from cannibalised Mk.IV bits.
3. Now the 12 SQN "NH" codes are well and truly fictitious- and I remember this was well known back in the 1960s when the museum owner Harold Thomas painted them on. He wanted something easy with straight lines and no tricky curves - hence the fictitious NH-Y. He may be turning in his grave to know he has caused this controversy over his prized exhibit.
A shame you can't get out Danny, and put your finger on all the bogus Mk.IV components...