People act like something can't be both retro and a surprise.
Never forget that the Mr. Game & Watch, R.O.B., and Duck Hunt amiibo release was officially billed as the Retro 3 Pack. At least from a marketing standpoint, the term has been officially used to refer to more than just the Ice Climbers. Nintendo is more than obviously aware of the fan perception toward these types of characters.
Words have meaning, even colloquially. In terms of Smash, folks like Simon, Banjo, and Pac-Man absolutely do not fit the retro label any more than Mario or Samus do. As far as the Smash definition is concerned, you didn't need to just exist back in the 80's-and-maybe-early-90's. You need to have only existed then. The Ice Climbers are that. Pit, outside of ports, was that before Uprising. The three members of the self-titled Retro 3 Pack were that.