I have a feeling the Mullard name was put out to pasture once valve and maybe oscilloscope CRTs were stopped. The whole back-story of european tube manufacture is fascinating as Philips is just so dominent and either owned brands like Mullard or made tubes that ended up with a whole raft of brand names. The etched codes on these vintage tubes is where to start as many different factories had the same plate tooling and construction techniques, e.g. you can find examples of say a I63 ECC83 made in Blackburn or Mitcham branded Mullard, and also find French made ones branded the same, and then you can find the same tubes branded Brimar, Amperex, Mazda, Telefunken etc. It is a minefield, but the thing to read is always the etched code, not the logo! That tells you where the tube was made and when, though even then it can be pretty baffling!
As an example a have a number of Brimar labelled E83CCs which are unlike any UK plate design. I eventually figured out they were re-badged US Sylvania tubes, which made no sense until I found out that Philips bought Sylvania sometime in the 1970s in order to grab an active US defence contract. Philips/Mullard made Brimar tubes, so some NOS examples ending up labelled as such makes complete sense!