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. 
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Ah, yes the "magical midrange." I agree. Yet in my Blackburn, the mids and upper mids seem over-emphasized. I prefer to tone it down a notch or up the bass and midbass. Could be a mismatch with my system, I suppose. Does the Mitcham have as much detail and air? 
I use RAM 6922's in my ARC phono amp and they are by far the best tubes I have ever used.