I stick to a main theme for most characters and then reuse them as they feel relevant.
I dont remember most of Ender's old unit names, but he's been using the Death Berserkers as his unit for a long time now. I like to think its the same rabble that just keeps growing or losing random men as time goes on. My Trinity followers, when they've had units, typically use some name referencing that and whatever god they prefer (Judgement of Alluran, Khagister's Wrath, etc). My trader has used the same theme, but with regional variations depending on his locations since I started playing him. It's usually East <Insert Region> Trading Co., though recently its just been Fatmilak Trading Co when he bothers to carry a guard.
A while back I had one of my characters who was the lord of Tepmona just use 1st Tepmonan Guard, and then the number changed every time he recruited a new unit. I think he was somewhere around the 15th Tepmonan Guard when the demons finally slaughtered the poor guy.