Wow, Ken...you ARE a glutton for punishment, aren't you.

Keep in mind that the old cutlery companies cranked out hundreds of those knives and they figured out ways to simplify complicated mechanics with mass production. We do things the hard way compared to them even though our tools are more advanced. Mind boggling if you think about it. Good luck with the sportsmans knife.
On the seal cap pruner, they were indeed refered to as "seal caps". Some speculation was done above and, although no one knows THE answer as to the reasoning behind their purpose, the seal cap surely had a purpose. Tony and I were talking about it earlier today and here's some other ideas for them:
1. They allow the knife handle to be shaped by the stag that is used. Ken, you pretty much answered this question above when you said it looked like a lot of the old pruner handle shapes were based on the shape of the stag. Make the cap fit the end of the stag and you have a finished knife...no wasted stag goodness

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2. Saves expensive steel. Anyone that cuts parts out to make a knife would figure this out pretty quickly. The back end of a knife spring is a pretty good sized chunk of steel that could be made of something much cheaper. The seal cap replaces that.
3. It "seals" the end of the stag. Look at almost any old kitchen cutlery set....seal caps.
I don't think they were made to be used as hammers. Any seal cap knife I have seen that was used that way was damaged. Maybe light crushing or pressing with the end but hammering, no.
Here's a couple images from old catalogs where they are refered to as "seal cap". I have seen other catalogs where they were just refered to as "brass cap" or "steel cap".