Here is my $.02
I've been in the LED signage industry for 12 years, as a senior technician and R&D lead.
There is a tremendous amount of difference between LED grades and manufacturers.
Here's a specific story:
My company produced white LED gas price digit displays for the Mexico Market. Everything worked great on the product samples and at test sites in the US. 2 months later, started getting reports of multiple failures of the LEDs. This first batch was supposed to have used Cree chip sets.
Our board manufacturer whose responsibility it was to install the LEDs claimed it was an issue within receiving a batch of counterfeit LEDs, meaning that they were actually toy grade rather than the LED we were expecting. Who knows what really happend. On my scope, the looked like genuine Cree chips, and had the same voltage drop as the Cree chip we speced.
On the next we speced Epistar, a Taiwan LED. However we still had failures.
Third try, we got the highest grade that Epistar had. Still less failure, but one or two LED lights on a fixture or having premature degradation still made the product look horrible and required a replacement.
Fourth try, we used Nichia from Japan. 10x the cost, but they actually worked.
Of course with 10 times the cost, we priced our selves out of that market.
So yes, there are absolutely different quality LEDs even though the front page of the specification sheet may look the same.