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. 
Tvad... On the contrary, I'm "satisfied" with most of the 6922s I've tried. Each has its own character and I appreciate their respective ways with music. On occasion I change tubes when listening to particular types of music. My generalist tubes thus far are the Amperex USA 6922 D-getter and the early Siemens e88cc. There are still mnay I haven't tried. What fun. Re the Mullard, maybe I got an inferior tube...
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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?