My guess, and that's all it is
, is that the black either wore off the trim, or some of it came off and the owner decided to remove the rest of it, or an owner decided he liked bright trim better and removed it for that reason. Maybe even some new buyers might have requested the dealer replace the black with bright trims. Black trims were a new thing, and not everybody liked it. Same thing happened to late 70's Trans Ams.