Ah - didn't know that. So the previous breastplates were what - darker, like those in the 1990's knights and squire sets?
These breastplate first appeared here in the late 70's 3291 - Nuremburg GuardsAnd then, they were reproduced for 3329x - Knight And Squires with the darker colour!The 4666 is probably the first set that we see these light grey coloured breastplate, as Vauban points out!
and the dotted version in 4567??