An external audit has found the extent of the overspend on the 2017 event is far higher than the $100,000 minimum figure ACT government officials gave during Estimates hearings last month.

Fairfax Media can also reveal the 2016 festival ran almost $940,000 over budget, a stark difference to the 2015 event, which came in $200,000 under budget.

It can also be revealed the territory government recovered nearly half the overspend for the 2017 festival through the National Capital Authority.

The directorate has released part of the audit, which began in May after anomalies between the paid invoices and the expected budget were picked up soon after the event concluded last October.

Audit firm Protiviti found there was no contracts register for the event, a lack of appropriate procurement activities and controls, inadequate contract managements and few contracts in place for significant expenditure.

It also found there were payments outside of contracted amounts, unsigned contracts or memorandums of understanding, no event-specific financial reporting, and a lack of reconciliation and review of revenue sources.

The review found there was possible calculation errors made in a budget spreadsheet that was maintained separately to the financial management system, that meant there was a "possible misunderstanding" that the budget for the event was $4.04 million, nearly $1 million more than it actually was.

"This could have contributed to the overspend," the audit said.

However the auditors detected no hint of fraud, which Chief Minister, Treasury and Economic Development Directorate Deputy Director-General Kareena Arthy told the Estimates committee was an open question.

As the audit proceeded though, Protiviti said it became obvious it did not have the scope to properly identify all the deficiencies in the financial management of the event that contributed to the overspend.

The auditors also noted they were not conducting a forensic investigation purposefully to sniff out possible criminal behaviour, and there had been nearly a complete staffing change since the event, which meant they could not get answers to some questions.

They recommended the directorate conduct a specific review of procurement processes and controls given the serious deficiencies identified in their audit, re-assess the value-for-money of longstanding Floriade contracts and establish a suite of budget and financial reports for the event.

Acting director of Events ACT Jo Verden said as a result of the overspend, a new senior executive position had been created to oversee events, and more rigorous staff training in procurement and contract management had begun.

"Further changes to budget oversight and delegations has been introduced to address some of the issues that have subsequently been raised in the review," Ms Verden said.

Ms Verden said while the overspend had been identified as early as last October, it was not possible for the events division to determine with any confidence how far over budget they'd gone, hence the external audit.

"The overspend on Floriade 2017 was first detected in October 2017 once invoices relating to the event were processed and comparisons were made against the expected budget allocated to the event," Ms Verden said.

"At that point, the event had been delivered and expenditure was already committed. Additional revenue achieved from Floriade 2017 and Enlighten 2018 has partially offset the overspend on Floriade 2017.

"Measures were put in place for the 2017 event to reduce expenses. Changes to the event footprint resulted in reduced car park access costs of $89,803.64, charged by the National Capital Authority. Events ACT was also able to negotiate a waiver of $587,035 from the National Capital Authority as part of a sponsorship arrangement."

Ms Verden said other events managed by Events ACT,  like New Year’s Eve in the City, Australia Day and Canberra Day, were not impacted as a result of the overspend.

She said a new team had been set up to deliver Floriade 2018, including an external event executive director.

Events firm Visabel signed a $150,000 contract in February to run the festival and conduct high-level planning for the 2019 event.

However Ms Verden disputed this meant that the total management of Floriade 2018 was outsourced - just one aspect.