Maoraigh1
My previous post as far as it can be relied upon does answer the question.
There is normally no limit to the accrued hours or years for private use but once over the TBO the private use will still require a licenced engineer to sign off the engine at the prescribed intervals. The 20% extension where applicable applies to hire and reward use when a Release to Service is required. I repeat: each engine type may be treated differently even the same engine type could fall fowl dependant on the engine serial number. Some engines cannot be extended at all other than for for private use. Therefore for an authoritative answer, for a particular engine, refer to a licensed engineer.