Doing my own research (spending more time than I care to mention), and also dragging information out of Celestion, who for some reason are kinda secretive with some info, I found this:My Bogner has ‘94 V30s in it, but I wanted something older and a little different. From the research I did, it seems that Celestion made the speaker in ‘86 and Marshall liked it so much that they inked a deal for exclusivity. I gotta say, I like them a lot more than I thought I would. They’re smoother and bigger sounding than most V30s IMO. I’ll see how they sound with a mic on ‘em, but it’s glorious in the room!
In 86, the Marshall Vintage was released as an exclusive OEM product. However, they also released their own Celestion branded Vintage 30 for aftermarket use. These where not the same speaker as the Marshall one. In the early 90s, they changed the manufacturing process for all Vintage 30s and their nearby relatives. Why? Probably to make them cheaper or easier to manufacture, no one knows. Mesa didn't like the tone of the new Celestion V30, so they requested and got the original spec V30 as an exclusive deal. This Mesa OEM version remained unchanged until the early 2000s, when product moved to China, and the rest is history.
And to anyone who doesn't know: Yes, the relocation to China did change the sound of all V30s and their cousins. The tooling equipment is the same, but the materials are not. That's why they sound different. The frame is made from a different metal composition, the magnet is also not the same etc.