Now that the vintage of your Nishiki Prestige is confirmed, I thought I'd post some pics of an '86 Prestige that passed through my hands, proving yours is definitely not an '86. I find the seatstay ends at the seatlug interesting, but wonder how strong they are. I also like the variation on the brake bridge.

Something I've noticed with mid to late 80s Nishikis vs. a couple 70s Nishikis that I've seen is that the paint on the older Nishikis is far superior. They seem to have had a prime coat that prevented rust when the top coat was chipped. On the other hand, the 80s Nishikis have all had bubbling rust at various locations on the frame, especially the BB joints. Of course, these have all been entry to mid level frames.