I am not an AI user but as an aquarist who has worked at an LFS and had multiple tanks, I think there are a few things to note with LED longevity.
1. 50,000 is under ideal conditions and may not materialize.
2. 50,000 is only the LEDs and it does not apply to the power supplies, fans, and other electrical components.
3. LED intensity is not just due to the LEDs. Temperature, Water clarity, and Optics will also affect the PAR the coral recieve.
With these facts in mind what I have often found is that in most cases the actual LEDs are the last thing to fail in a light fixture. Lenses, fans, power supplies, control transmitters, and other components are much more likely to fail. I find I get and average of 5 years out of an LED fixture. I have LED lights over my tank now that I purchased in 2012 so they certainly can last longer but I have also had fixtures die after only 3 years of use. The one thing that correlates the most to a short fixture lifespan in my experience is how close the light is to the water's surface. I have never personally had a fixture with burnt-out LEDs but I have had fans, power supplies, and electrical components fail.
It is very likely that the output of your lights will fade over time. This is not just because the LEDs loose efficiency but because lenses cloud, fans slow down or stop, heatsinks get coated in dust, and the power delivery from the board may diminish or be less consistent.
The first thing I would recommend is that you clean and inspect your fixture. Clean all of the dust-out and keep the lens as clean as possible. If a fan has stopped or a lens has permanent haziness then contact the manufacturer to see if you can get a replacement. Clean your lid and use carbon to keep your water clear. I believe this will cover the vast majority of light output degradation.
If you think your corals want more light then turn up your LEDs slowly but if everything looks happy even if the light output is lower then I wouldn't worry about it. I have made plenty of mistakes chasing perfect instead of good. If the tank looks good then enjoy it and don't stress.
If you really want to chase perfect then you should probably get a PAR meter.
