In this small Discussion, I want to help you guys with explaining the development of the Sellswords(Note, I will update this, when i am finding out more).

Sellsword Spearmen
v
Sellsword Men-At-Arms OR Sellsword Bardicher(Polearms)

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Sellsword Skirimish
v
Sellsword Archer OR Sellsword Crossbow man