gme – I am finding your request for advice difficult to understand but I will take a ‘stab’ at it …..
If a fence has accidentally been erected in the wrong place and a survey has determined that the fence has been erected in the wrong place then the fence should be relocated to the correct place. It should not matter how long that it has taken to discover the error. (Things get technically trickier after 12 years but that is another story!)
Not all land sizes need to be exactly the same to create an exact same entitlement. If you believe that your entitlement should be adjusted then you have the option to take this matter to the Tribunal.
See here for a legal opinion and a case note on changing unit entitlements:
https://lawyerschambers.com.au/what-are-unit-entitlements-and-can-they-be-changed/
See here for a legal opinion on changing boundary fence lines:
https://www.andersons.com.au/lawtalk/2015/june/the-law-and-encroachments/