All I can tell you Craig is that in '84, RWD Cadillacs got new "goldtone" ornamentation which included the taillamp escutcheons and outlining as well as the winged crests on front turn signal lenses. This style is identical to the chrome version of 82-83 except for the goldtone which is supposed to be correct from 84-86 as you noted. Note- it's "gold tone" not the 24K Gold Plated stuff used later which looks very different. The 84-86 finish actually looks more like bronze than gold. Beginning in 1987 the Brougham taillamp crests got filled in with the red/white/blue colors of the Cadillac crest and returned to chrome only, including the front "birds" on turn signal lenses. 1988 & 1989 were the same unless Gold Package was ordered.
Why the part number is the same of both versions (technically there were 4 from 1982-1989), is a mystery.
Hope this helps.