If I remember correctly (can't find links), but when the RAAF's CBR program was suspended at 10 airframes it was because of two reasons.
Firstly, the CBR program for each airframe was far more complicated, invasive and extensive than originally planned.
And secondly, that it was discovered that the centre barrels were 'not' as fatigues as first thought, hence the program being cut short.
Move forward a few years from that time, and I remember a couple of years ago that the DSTO came up with a 'new fatigue monitoring algorithm' that actually showed that the RAAF's Classic fleet was not as fatigued as first thought.
https://www.flightglobal.com/news/articles/australian-algorithm-extends-life-of-classic-horn-423803/
The relevant quote from the above article is:
"As a direct result of the upgrade of the Hornet monitoring program, the reprocessing of the entire fleet’s usage history indicates that fatigue is no longer the main driver to the planned withdrawal date,” says DSTO research leader Loris Molent."
Apart from the above from the Flight Global report above, I remember reading a more detailed report, maybe an ANAO report, that basically said that the airframes were a lot 'healthier' than first believed.