Yes, if they are over driven beyond the cooling capacity of the thermal design. I also think the flux BIN can change... at least these have been my observations with 1.4A drive circuits and the XRE.
This is why Surefire designs are a step down from their competition, in terms of Lumen output. Favoring longevity and reliability over Lumen output. This is also a BIG part of the premium $$ that goes into the Malkoff drop ins.
This is why I run my DX-MCE with non-IMR cells. Sure its not as bright, but it runs cooler, and I can just leave it ON and use it as a ~250L (ballpark) task light. Which is still VERY bright IMHO. I have owned this light for over a year and had it measured in two different spheres over that time span and its output has not dropped and its white tint has remained constant. In this setup it draws about 2.5A from the 18650.
The counter-argument could be made that an XPG in a 1.4A setup can easily obtain the samle OTF Lumens. But the XPG will be driven harder and closer to its thermal limit than the MCE... at that ~250L level.