I'm not sure of the rules in Canada, ST, but here(UK), engines are allowed to continue in use indefinitely beyond either their TBO/calendar lives + any % extensions granted.
This is subject to regular checks of the condition of the engine, and is restricted private use only. (No renting)
The problem is, when renters collect an aircraft, they have no way of knowing, short of asking to see the engine logbook, if the engine is 'on condition' or not.
MJ
