CV4109 mullard tubes

I was told the Mullard CV4109 are the premium grade of E188CC/7308 tubes. Does anyone have any knowledge about these CV4109 tubes by Mullard?
Here's the info I found:

Mullard CV4109 - 1966 Premium Grade Long Life E188CC CV4108 7308 Halo Getter Military Stock Mullard Mitcham Production - Gt. Britain
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