yes I appreciate that, but the poor £5/hr staff who do this job of sorting out the leds at the distributor's place may not pay too much attention to bin numbers....and why should they?, the bin numbers are not marked on the leds and so if they get it wrong , nobody will know.
Also, leds in parallel need really to be from the same batch....and if leds have been swapped around at the distributor's place then how do we know that one reel of leds is all from the same production batch? The production batch number is not marked on the reel, and it certainly is not marked on the leds.
The bin number is indeed on the reel, but if other leds have been swapped onto that reel from a quarter full reel elsewhere, then how do we really know if all the leds on the newly made up reel are really from the same bin?
I would say I would only trust the bin number on a reel if that reel was fresh from the led foundry itself.
I know it is not "politically correct" for me to suggest that people on low pay don't always pay attention to fine detail such as part numbers when they can get away with it, but I know of many workplace examples of this happening.