Scan through the pics for the auctions over at eBay. No difference than what I wrote. Here's the list of part numbers from the 44W Regal Parts Catalog. You can check the RPO codes on the SPID label.
25525744=84 Black Grille RPO TL6
25525744=85-86 Black Grille RPO BX1/TL6
25515915=84 Chrome Grille
25526036=85-86 Chrome Grille
25526035=85-86 Black Grille RPO TL6
25526613=87 Chrome Grille
25526614=87 Black Grille RPO TL6
All 85-87 GN/GNX will have both the BX1(No Hood Ornament) and TL6(Black Grille) codes which signifies that those grilles(except 1987) are GN specific.Basically the 84-86 GN Black Grille was the 84 Regal Chrome Grille painted black on the spokes. Now there is a blooper floating around out there. Buick released a press photo of the 1985 GN which showed the 85-86 Chrome Grille painted black with the wider spokes left chrome. I believe that Buick wanted to keep this theme of the painted chrome grilles going to distinguish the difference between the years but for some reason the GN grille was never changed and the 85-86 T-Type grille had these exposed chrome spokes painted black. Which is strange indeed because if you're real sharp you can spot what year any Regal is just by the details of the grille and front panel. You can even tell the difference between the 85-86 T-Type although they share the same grille. The 85 has side marker lamps that have a silver painted border where as the 86 uses chrome border side marker lamps. Like I said if you're sharp you can tell what year any Regal is just by looking at the details. Even with the 84-86 GNs.