For decades, it was assumed that so long as we did not exceed yield at any KT location, we did not have a fatigue limit. But I've heard that some of the larger engine manufacturers have now spent enough time and money collecting enough data to know that is not entirely true; but I've never had access to this data.
But the fact of the matter is that every engine flying has places on critical components operating at or above yield. (Naturally, "above yield" is not entirely true because the metal will yield and redistribute the loads so as to not exceed yield.) So every engine flying will have a fatique life and a creep life, both of which can be seriously shortened depending on the actual load cycle the pilots apply to the engines. A single 50 degree F over temp event can cut these numbers by half or more. (Keep in mind that max turbine temps are typically several hundred degrees higher than the melting temperatures of the alloys they make the engine out of.) Required overhaul periods are planned around these limits, and actual cycles are tracked carefully. They also do periodic bore scope inspections to determine that no cracks exceed their critial acceptable length.
A really exciting new technology will monitor an engine full time the entire time the engine is operating. It knows the condition of every blade during every revolution of the engine, and can sound alarms when micro cracks so the engine can be shut down for an overhaul before it explodes. So far, these are only being put on industrial gas turbines because the fly boys don't like the extra weight. But my opinion is that it will soon find itself into the aviation market. So if the calculations say to overhaul the engine at 5000 hours, real time condition monitoring might let you get much more time between expensive overhauls.