My previous set of road shift cables (Shimano, not sure of the exact model) included one special ferrule that has a much thinner section of ferrule sticking out past the end, and a keying ridge on the side meant to slot into the last housing boss before the rear derailleur.
It's the lower one in this picture:
Here it is installed, no cable:
What role does that special ferrule serve?
Is it critical or just a nice to have?
I'm replacing the housing with Jagwire and I just got generic plastic ferrules for all the shift housing ends, like the upper one shown above, so I don't have a fresh one of those special ferrules.
Based on answers to the above, should I replace the special ferrule with a fresh generic one? Or reuse the old special one in that location despite it being about 5 yrs/ 10,000km old? The compression wires of the old housing are extruded by about 1mm, which I usually take as an indication the ferrule should be replaced (especially if plastic):