From looking at my small collection of caps, one Stant and several repos, this is what I found. looking at the underside , the wall section of the ribbed outside rim is noticeably thinner on a real one. Mine measures 0.050. the repos are thicker 0.08 to 0.095 inches and do look much thicker. The thinner wall of the real one would be consistent with keeping material usage down for high volume production and the use of high quality tooling. The repos are thicker wall as you typically see in low grade tooling and die casting. If you look at the examples noted above, the real one is nice and thin and the repo just looks clunky and thick. The next item is easy to spot and that is how the "fin" rolls out over the edge to meet the rim. On a real one the fin rolls over in a smooth transition to the ribbed rim surface. On a repo , there is a witness line on each side of the fin where an insert is fitted into the mold. This is all part of low quality tooling. As to the equal versus unequal tabs on the stamped piece, I don't think this matters as it is part of the assembly and easily removed and changed when replacing the red gasket. Of course the Stant circle logo is a dead giveaway.
All of them look good installed on the car, although more than half of them are on backwards!
Just my opinion,
(David's answer will be the correct one)