[Captain Nash]

Classic is generally their first "long running" design, to me. If a character has an outfit for a couple of appearances but then shows up after that with another new outfit that newer outfit may become their classic design (like FA Wolverine vs. GSXM Wolverine as one example.)

There are exceptions to that if there's a team that all appeared in cohesively similarly designed outfits but later on yet still early in their career develop unique outfits - examples being the original 5 X-Men. None of the yellow black/blue outfits they wore would be considered "classic" to me...too generic.

Also Wasp is a major exception to this as she had a litany of outfits early on. There's not really one look she stuck with overwhelmingly to be considered classic.

Classic is NOT the same to me though as iconic, which would be their best known look. Carol Danvers - Captain Marvel/Ms Marvel for example- the original custom is classic but the black/yellow outfit is what's more iconic to me.