A significant proportion of the state's heritage boundaries are believed to have been incorrectly recorded and it's predicted the issue may take Heritage Tasmania staff up to 15 years to completely fix.
These boundaries - known as cadastral boundaries - are used to determine whether or not a development application is required for the owner of a heritage-listed property to build, demolish or change something on that property.
If there's any risk that the heritage values of the place could be affected by works, then the owner is required to submit a development application to their local council.
The application is then forwarded on to the Tasmanian Heritage Council, which makes the final decision on whether the work should be allowed or disallowed.
There are more than 5000 properties listed on the Tasmanian Heritage Register.
If cadastral boundaries are recorded incorrectly, it could lead to challenges being made through the Resource Management and Planning Appeal Tribunal.
And it's now been revealed through an audit detailed in a Right to Information decision that "boundary confidence" for the THR was measured at only 76 per cent. One criterion for this category included whether or not the boundary was defined as per the requirements of the Historic Cultural Heritage Act.
Just 25.5 per cent of the THR's datasheets were deemed to be acceptable.
The Heritage Council has been working to create a new boundary overlay for properties on the THR - and, in the process of doing this work, it's found that a "high number of boundary issues" exist in its data.
In the RTI decision published on Thursday evening on the Primary Industries, Parks, Water and Environment Department's website, more than 200 pages of documents were released relating to the audit of location data on THR entries.
The audit commenced in 2016 and was completed in 2018, although some properties in Launceston and Hobart still need to be reviewed.
Emails dating back to 2016 are included in the documents, seen by The Examiner. Most of these were exchanged between Heritage Tasmania data and geospatial coordinator John Stephenson and senior Heritage Tasmania staff.
In one email addressed to Heritage Tasmania registration manager Annita Waghorn on March 28, 2017, Mr Stephenson admits that "the audit has confirmed that our data is not great".
One particular note from Mr Stephenson regarding a "high profile registration" describes the property's datasheet as "embarrassingly minimal".
The audit has confirmed that our data is not great.John Stephenson, Heritage Tasmania data and geospatial coordinator
Another email from Mr Stephenson to Ms Waghorn - dated December 19, 2016 - said that if the findings in the pilot audit were extrapolated to the entirety of the THR, more than 3000 datasheets would need to be updated, which would take a staggering 15 years for the registration team to do "at its current staffing levels".
In the same email, Mr Stephenson wrote that the pilot audit found the required replacement entries in the THR would take four years to complete.
A DPIPWE spokesperson told The Examiner that the audit had found about 850 entries in the THR required amendment or revision.
"This work has commenced and is continuing," the spokesperson said in a statement.
"Measures [are] being employed by the Heritage Council to enhance the register.
"The audit highlighted that many of the earliest entries were lacking in detail or had location issues that need to be addressed, including subdivision and title changes."
According to the spokesperson, 377 THR entries were amended and/or revised in the 2017-18 financial year.
"In 2014 amendments to the Historic Cultural Heritage Act ... ensured all entries at that time were validated to remove any doubt about their legal status," they said.
"It is recognised that location details for places will continue to change (for example as a result of subdivisions) and the Heritage Council will address these changes."