I think your take is spot on. The shank splice is definitely Dunhill's work (original nomenclature ground off & re-stamped), and the bottom plug almost certainly, too. Once the bowl popped, though, Dunhill likely bailed and improvisation took over.
I'd love to send a time-traveling fly-on-the-wall back to the day it was returned to Dunhill for that last time, in pieces yet again. Would have sounded like something of a Monty Python skit amongst the workers, I imagine.
Adding another layer of odd is how even after all that, when the pipe finally died for good, it still wasn't binned. Someone kept it in a drawer or trunk for decades.
My favorite storyline:
The pipe was a gift from some man's wife or sweetheart who unexpectedly died, and was the only object the man had left because her possessions were all lost in the house fire that took her.
But he was a laborer who worked outdoors, sometimes in harsh conditions, and despite his best efforts the wind and various fumblings and accidents kept diminishing his treasure. To NOT smoke it, though, was unthinkable. That would be surrender.
So back to Dunhill it kept going, and when they'd had enough a local repairman did his best, and after many years the man himself finally passed away.
The pipe, when found decades later, was in a tattered silk bag with a hand written note, "From my Emma".
The eBay scrounger who came across it, though, wasn't a sentimental sort and only saw a couple pounds, so the bag and note were thrown away without a thought.
Then, against astronomical odds, along came Ken.
And here we are.