The backlog peaked at 320 nominated places or object in 2008 that had not been assessed and has been reduced, but still stands at about 136 nominations at the end of June last year - the latest figures the territory government would provide.

But the delays the backlog is causing has prompted calls from the Kingston and Barton Residents Group, among others, for the government to update heritage listings for several landmarks across the inner south to include the social contribution of the buildings.

Among them, the group has urged the listings for Telopea Park, Manuka Pool, Manuka Oval precinct, the Forrest Fire Station and the Kingston shops be updated.

KBRG president Rebecca Scouller said there was no "conservation management plan" for Telopea Park or Manuka Pool, while a draft conservation management plan (CMP) for Manuka Oval precinct "had been stagnant for some time.

She said a further nomination lodged as long as 15 years ago for the Kingston Shops had still not been officially assessed.

While a spokesman for the Environment and Planning directorate said a CMP was being developed for "Manuka Circle Precinct", which included the oval, pool and Manuka Arts Centre, he would not say when it was expected to be completed.

"The current priority for the ACT Heritage Council is assessing the existing backlog of nominations to the ACT Heritage Register to provide certainty to the heritage status of nominated places and objects, however the council amended the registration details for one place in 2016," he said.

"The council and ACT Government have invested considerable resources in addressing the backlog of nominated places and objects."

But CMPs are not statutory requirements and it is unclear what order of priority is given to developing such plans, as the "taskforce" meant to consider them did not meet at all in 2015-16.

National Trust ACT heritage committee member Eric Martin said delays were common in both official heritage assessments and conservation management plans.

He said there were a raft of problems with the territory's heritage system, including that the original reason for nominations was not released publicly before an assessment was made, leaving both property owners and the public in the dark.

"There's frustration all around, it's not just Trust people or people concerned about heritage, it's also property owners and developers because they face uncertainty as well," he said.

"There's no doubt there's been some buildings nominated to the register that have also been demolished before an assessment was completed - there was one in Forrest nominated for its architecture that was demolished a few years ago."

Ms Scouller said the residents group was also concerned some of those buildings and areas already listed on the register, such as Manuka Pool, which attracts about 30,000 people a year, were deteriorating, an issue Friends of Manuka Pool have also urged be addressed.

"If heritage listings are not formalised then they have minimal protection and we might lose them, like the old Capitol Theatre, if there is no investment in maintenance then we might also lose them," she said.

"The loss isn't just physical but also has social impacts; imagine if we lost Manuka Pool."

Long-standing heritage concerns have been exacerbated since the unsolicited bid from Grocon and GWS to redevelop Manuka Oval, which the government has since rejected.

"Part of becoming the 'coolest little capital' is celebrating where we came from while looking to the future," Ms Scouller said.

"This doesn't mean locking up heritage sites, but re-purposing them and embracing what they add to the character of our older suburbs and to our social spaces."

The residents group acknowledged recent investments in Manuka Pool, but Ms Scouller said it still needed a "significant funding injection".

"It is an iconic part of Canberra's present and past and it is a shame to watch it slowly deteriorate, hopefully not beyond repair," she said.

Ms Scouller said the group understood there were "budget constraints" on the government.

But she said they were calling for a commitment to continue progress on heritage issue "as part of the broader budget plans to increase business, tourism and social amenity in the inner south".

The government spokesman said that an assessment of how long it would take to clear the backlog could not be made, given it changed from year to year as new nominations were made and older assessments completed, and some nominations, such as for precincts could take "several years to assess".