I think the onset of war was something of a 'lucky break' for the company as it had been developing the manufacturing process for a couple of years prior to 1939. During the war years the product was in great demand especially in the US and that's really how the company became a market leader since there doesn't seem to have been any serious competition. There was of course a huge blanket of secrecy over the exact process used for making Multicore™ and it must have been a real technical challenge at the time. I've never been able to find out precisely how it was done but it's interesting that two more cores were added during the early 1950s by which time there must have been a significant R&D budget. I think the advertisements displayed here make entertaining reading for anyone who enjoys a bit of history relating to our interest:
https://www.gracesguide.co.uk/Multicore_Solders
Alan