As I said in my email to you, the Plus version was simply a substitute to make up for the shortage of IIFDs caused by Yamaha installing E! from the factory. There may have been some IID Plus models with E! in them, but that would be a very rare model, any DX7II that had E! installed at the factory had a large E! logo on the front panel near the DX7II logo. If E! was added aftermarket by a user it might not have had the E! logo, but you would notice things in the menus/lcd screen that should not be there on a standard IID, like Octal mode, sE!quencer, etc.
DX7IIFD, SY77, SY99, Hammond C3, Steinway L, CP300, AW1600, etc.