Typical diode lifetimes are in the range of 25,000 to 50,000 hours. If not, it's very possible as you say that the diode has degraded to the point where power loss is very noticeable. I suggest you read this Topic for some additional perspective: There's nothing magical about the 100% number that damages diodes. However, there are reasons for running below 100%. Honestly, it depends on several factors, and there is no simple chart to cover everything. In this post, we'll explore the factors affecting a diode laser's lifespan and how you can extend it for optimal performance.