I’d recommend paying the Cree website a visit and look at the specs for their current emitters, it is very enlightening [no pun intended]. If you look at the various binning data you’ll find wide variation for any U2, T6, S2, R5 emitter. Some emitter bins consist of dozens of various chromacity [tint] groups.
Look at page 8 of the Cree XM-L specs
The U2 bin consists of nearly 3 dozen discrete tint groups. If you look at the first pages it explains all the coding used to identify emitters when ordered for production work. I agree w/ Bort, it would be nice if Cree could incorporate coding on the emitter so you could verify exactly what you were getting.