...and London Prides that are pre-war or just a bit after the war...
Minor point, but for the record I don't believe there are pre-war London Prides. The trademark filings were post-war in the UK, Canada, and the US, and the "first use" dates cited were after the war. Moreover as I recall there are no mentions of the London Pride in trade journals until after the war (although this is something I'll verify when I'm back home), whereas mentions of every other major offering in the line-up are frequent.
Announcement of the new Comoy's Blue Riband line of pipes from 1938
This was actually published in the September 1939 issue of
Tobacco not 1938. So the chronology for this limited dataset is the patent was applied for on Nov 8, 1938 (after provisional specifications were left on Oct 28, 1938), the trade notice about the Blue Riband mentioning the inter-steel was published in Sept 1939, the complete specs were left at the patent office on Oct 20, 1939, and the complete specs were accepted on May 13, 1940.
Over and above this I seem to recall finding an informative trade notice from the late thirties specifically about the intersteel; if I can dig it up when I'm home I'll post it.
More broadly speaking it's my recollection (although I haven't looked at this question in years) that the intersteel was used in all the Comoy-branded models from its introduction shortly before the war until output was hampered by lack of raw material and the reallocation of labor and facilities to the production of war goods. The intersteel was also used after the war in a number of models, although how long the latter period lasted offhand I can't say.