Sablebrush gave some superb information about the nature of the stems on the three pipes which were the original topic of this thread. I learnt a lot, and was fascinated by the whole insight he afforded us all.
Well, I found two more pipes, and, they fit into this narrative - midway between pipes two and three, above.
I'll call these four and five. Four (top) is dated 1913, and five is 1917.
Both pipe's stems have a condenser. But rather than being made of bone, as in pipe two, they are moulded from the vulcanite and are an integral part of the stem. It seems they are an evolutionary step towards the ultimate removal of the condenser and arriving at the simple push tenon stem of pipe three.
A final note: it's very hard, if not impossible, to see, but they have a very slight flare at the entrance to the condenser. This is a tip of the hat to the bone condenser of pipe two, with its obvious flare.
The historically significant trio now becomes a quintet.