Authentic Epic and clone SMPL mods are almost indistinguishable. The button is a little different, but IME a $9 clone is 99% 1:1 to the $100 authentic. If you do a search, there are pics that show the differences side by side. The firing button venting is really the only difference and some could argue the clones are vented better. Some clones have a pressure fit top as well and the clearcoat helps make it look like a one piece.
Unless you paid $80-120 for the SMPL, I would bet it is a clone. My copper clone SMPL doesn't patina either. My authentic SMPL was brass and it tarnished, but so did my brass clone.
I'm not sure if an authentic SMPL tarnishes, but a quick search should tell you immediately....