Uh, the SE came out in 1987, March to be exact, along with the Mac II.
Either way, I would vote for a MacPlus prototype before the case was modified by Frogdesign, if it has the same square badge recess for the 128K/512K. Did it have the horizontal Snow White lines across the front and the vertical lined skirt around the base that distinguish the SE? The SE was designed from the ground up so there would have never been a prototype that used the older case style.