operated privately all the time beyond the TBO limits of the manufacturer
Well, there's a difference...
the TBO "limits" to which you refer, are generally "recommended" in the maintenance manual. The overhaul time limits on dynamic helicopter components are the subject of an airworthiness limitation, and are not subject to negotiation or extension.
An operator or maintainer sometimes has the opportunity to maintain an aircraft under a system which differs from the manufacturer's recommended practices, and thus sidestep a recommended overhaul time, when an alternative "system" provides for an airworthy aircraft.
Airworthiness limitations are different. When you exceed the limit (hours in service) that aircraft is no longer airworthy.
It's all a matter of how
a limit is expressed...