Help needed on Blue Tang with black (parasitic?) issue.

[Mr. Seahorse]

Hi,
I am posting this on behalf of another person. They have had this blue tang for 2 years. For the past few months it has developed these black marks on the blue sections.
What is it? Any help would be appreciated

Thanks

 

[Coral reefer]

Sure seems like some HLLE. Not sure if there’s more going on or it’s the worst case I’ve seen.
Head and lateral line erosion

 

[PjFish]

Those Vermetidae Snails in the tank can cause lacerations that look similar if the fish is rubbing on them.. Have him crank the white lights up and take better zoomed in pics..Hope it's not HLLE.. Are those scars from healed wounds or current open wounds?