Is there evidence for this? Measurements etc? There were similar rumors about the HD 800 to have different tunings over the years but nothing I read or experienced made it true. I listened to a 6xxx S/N, my 13xxx and high 40k and found no differences with the same pads.
I've been profiling headphones in commercial recording studios with Sonarworks for years. Open back HPs aren't usable in most tracking situations so we typically use Beyer DT 770 Pro or Sennheiser HD 280 Pro that have been calibrated.
Many artists, particularly string players love to come into the control room and hear playback on HPs (in addition to room corrected near field and mid field studio monitors) because of the intimacy they provide with their own playing. They can catch subtle string / fret noise, intonation issues in their own playing, for example.
We switch to open back HPs at this point because as a whole they provide better sound. The HD800 were an immediate favorite and I've bought several pair over the years, so early production up to the latest production. We run 4 profile recordings to allow for any subtle variation in mic movement and then average them to create to profile we correct from.
We've use a calibrated Earthworks mic as well as Sonarworks own individually calibrated mic. We track these initial profiles at 96K in ProTools which is 32 bit internally. Mic preamp is a
GML 2032. D/A converter is a
Crane Song Solaris. A reference in pro studios and mastering.
We have seen no differences between early production HD800 and the latest in our profiling. Granted our sample set has been small, but 3 were early production and 4 were recent.
The HD800s has quickly become my preference and I've bought a second pair for personal listening at home. Both pair profiled exactly the same.