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. 
The Blackburn Mullard is fully burned in. The weakness of the tube is the anemic bass and midbass, producing an unbalanced sound spectrum. The upper mids and highs are glorious, however, detailed, harmonically layered, 3-dimensional and natural sounding -- among the best I have heard. This tube is great for a narrow range of music (in my system), but not for general use. For instance, a soundtrack of nature sounds from the forests and savannas of Africa is the most layered and natural sounding that have heard thus far. I use this recording as a test for soundstage and imaging. Another downside of the Mullard is a more restricted dynamic range compared to a Siemens 6922. I wonder if the Mitcham production fills in the bottom frequency range, offering as detailed but more balanced sound.
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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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tvad... Have you compared the Blackburn and Mitcham e88ccs?