Treyarch devs mentioned something about that in BO7, we were going to see different places in the dark aether, taking place in different time periods and eras.
So what if every member of the new crew is from a different era?
Takeo has like a samurai armour so he can come from that period
Dempsey looks like he can come from the cold war era, having like a Vietnam war type of outfit
Richtofen fits more in the classic WW2 era with this medals
Nikolai is the most similar one to this primis counterpart, so i would say he's from the same era as his primis version, which is a WW1 era