Here is that thread about features on a Mirage that I was looking to find before:
http://forums.h-body.org/viewtopic.php?f=1&t=27679
Seems like the bottom line though is that there is really no tie between VIN and whether it is a "real" Mirage or not. The door sill and the doors with the sticker may not even be on the car anymore. Maybe that "overspray" in the cowl can still be seen?
Anyway, what do you plan on doing with it? That's the more interesting question! Are you planning to do a Mirage restoration or something else?
Terry