NBN Co has seen a massive jump in the number of users in need of complex “custom remediation” of their services, up from 52 in April last year to 723 today.

The 1290 percent increase in open custom remediation cases coincides with the network moving into the final phase of construction - one that was always thought would include the most hard-to-connect premises.

Custom remediation works are complex and can involve the replacement of long cable runs, additional construction work, and “even a complete redesign to another technology”, NBN Co said.

NBN Co said overnight that it has opened a total of 723 custom remediation cases. Of those, only 10 have been completed, and the rest remain open.

Last time it reported this figure in April 2018, it had just 52 cases open and none had been completed.

NBN Co said that its WBA3 wholesale broadband agreement, many of the terms of which are currently subject to a regulatory investigation, afforded it two years to resolve 90 percent of cases.

There was no upper limit on how long NBN Co could take to fix the others.

“This timeframe allows NBN Co to conduct detailed investigation, and custom design and build works on a case-by-case basis to remediate premises,” the network builder argued.

But the time NBN Co takes to fix the problems is contentious.

The Australian Competition and Consumer Commission (ACCC) noted in 2017 that Telstra was advocating for much more expedient outcomes for affected users.

“Telstra suggests that ... a maximum timeframe of 120 business days should be set for a custom remediation solution (at present, no timeframe is included for a custom remediation solution),” the ACCC noted. [pdf]