Mitchum or Blackburn for the Mullard 6922?

Do Mitchum production and Blackburn production sound different in the Mullard 6922? I believe I once read somewhere that Mitchum made tubes for the military, whereas Blackbutn did not, so, presumably, with better materials and/or tighter tolerances or testing. 
Wow, it took a long time --150 hrs or so -- for my Mullard e88cc to break in. Now the bass is fleshed out, the highs smoother and soundstage more dimensional. Altogether a more balanced sound. Yes, magical, richly satturated midrange, if without the razor sharp delineation of the Siemens -- a wetter, more romantic sound. It's certainly a keeper, at least for certain kinds of music..