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Where a character is depicted in promotional material, such as ads, teasers, covers of compilations, figures, etc. wearing clothes they don't ever actually wear in canon. Examples include this Jonathan Joestar figurine (and artwork) in this bizarre green monstrosity or this◊ adult Goku figurine where he's decked out completely in Capsule Corp. swag.
I think the Jojo's example is, partially, based on something he wore for one chapter as a disguise and then never again, so it could also be a broader trope of assigning a character an "iconic" outfit based on something they wore once, if they aren't just making it up wholesale.