As on who was there 25 years ago (Ayres Rock), and another 6000 hours in Northern GA, the statement as put, that it was normal practice by operators to under record maintenance hours is unmitigated rubbish.
A kind view might be that the standard practice of using clock time (or a nominal .1 extra above tachometer time) for the log book has confused some people.
Under recording of maintenance hours, when it did happen was confined to fly by nighters from down south with cross hired aircraft,so as to rob the owner!
This almost always came unstuck when the aircraft arrived at a maintenance hangar for a 100 hourly falling to bits.
Infamously, a Robertson helicopter operator did try this on with his own fleet. Once suspected, CASA was spoiled for evidence with the simple expedient of cross referencing fuel bills, invoices for work and pilot log books. The ramifications were severe.