Using Asymetrical Shoulders will show-up on mission-costumes/disguises such as Personal Stories if your body type matches the replacement while using an aysm-shoulder

[Cobalt Arachne]

If you're using asym-shoulder options on a body type (female body character with female mission disguise) that matches the body of a model replacement using a player-based model in missions such as Eagle Eye's undercover Skull mission, Halloween costumes, or certain Personal Missions; Those shoulders will appear on the models. Even if that model comes with shoulders already.

However, the asym-shoulders don't seem to appear on costumes that are using NPC-exclusive costume pieces; Such as Anti-Matter, suspect that NPC-specific models use a different body 'category' than the standard Male, Female, Huge player sets.

Assuming this is because Shoulder, Right Shoulder, and Left Shoulder are three separate costume piece slots, and the latter two did not exist when these in-mission model replacements were made.

Screenshot #1: Skull Disguise in Eagle Eye's mission arc.
Screenshot #2: Heather Townshend in her personal story.
Screenshot #3: The Center in his personal story.
Screenshot #4: Anti-Matter in his personal story; Note, no shoulder.
Screenshot #5: Max in his personal story; Note, asym-shoulder goes over his Vanguard shoulders.
Screenshot #6: Verified on Deadlock during his story to confirm all three body types are affected.
Screenshot #7: Works on Prestige/Halloween costume powers only if they are based on player-model and don't NPC-only parts.

Will update this post if any new info is found or specifics. 

+Happens on all three body types.
+Correction: Happens on player costume powers such as Halloween/Prestige if they are using Player model as the base such as Legacy Chain

Credit to Lines for providing me with additional screenshots/testing verification.
 

Edited November 15, 2020 by Nayreia / Karonax
Adding clarification and screenshots