Due to multiple name of mob in game, there is specification:
White Crow Starshina level 33 in Northfields isn't boss build and hasn't rare drop.
White Crow Starshina level 39 boss in Raven's Roost has rare drop, armor called White Crow Body Armor. He can spawn anywhere in circle around Raven's Roost instead White Crow Vojak or White Crow Soldat (Serendipity Mob).
White Crow Starshina level 45 Veterans appear only during mission Beginning of Things Ending if you are level 40-49 and haven't rare drop.