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. 
Branded IEC Mullard?
B5H3 is only the manufacturing date and plant, should have more digits for type of tube before those.
Are these numbers etched or same lettering as Mullard?
I have seen such tubes on eBay and they are Mullard made ones but not sure if rebranded or not.

I'll look for the other numbers in a while. The tube's fermenting in my dac at the moment and sounds rich, detailed, 3-dimensional and quiet.