The ">12" materials should not be showing up publicly, apologies for that. Moving the Corona Material Library to Cosmos is ongoing, and those should only be visible to developers while that is happening, so we'll get that fixed and have them properly hidden again soon.
If you open Cosmos from Corona, you should not see any materials that are specific to V-Ray or Vantage (those will only show up, or should, if you open Cosmos from V-Ray, and then Corona specific materials won't show up :) ). Just to check, you had Corona as active renderer, opened Cosmos from the Corona toolbar, but you saw "Metal Pattern N 5cm" as a material in the library?