Trap spring knives are more fantasy than fact. Very very few originals exist, and even those tend to be from later time periods - well into the 1800's, and then usually late 1800's.
The key "feature" on them is that ring/loop on the end. That identifies it as from a trap spring. Without that ring/loop, it could have been made from any piece of steel.
And the whole issue quickly gets ... tainted ... by modern fantasy/ninja fighting knives with that ring/loop on the end of the handle - so they can be "twirled" around your finger in a fight to show how "great" you are. Fantasy.
So once that loop is removed, that knife could have been made from any piece of steel. Plus most broken trap springs broke in the bend. The two parts then were easily converted to a hide scraper with minimal tools. Just grind on a rock to true up the end and sharpen it.
Trap spring knives do look nice and cool. But have little documentable history behind them. Plus a knife of any length really does require that you re-forge the whole spring. Half just ends up too short for a blade and handle.
Just my humble thoughts to share, and best used in conjunction with your own research.
Mikey - that grumpy ol' German blacksmith out in the Hinterlands