Barracuda tail light bucket

I removed the lenses from a 64/65 Valiant/Barracuda tail light assembly and noticed a translucent amber coating on the tail/brake light bucket but not the reverse light bucket. It was bubbling and flaking but it covered the entire bucket area. It was not present on the other tail light assembly. Was this some sought of coating that was applied when new to help the reflective/color properties of the light? It's as if bucket was coated with amber shellac. If this was a factory coating I would replicate it before reassembly.