Trying to find one little thing weird is not the way to authenticate these coins. The best way to learn how to authenticate coins is to look at a BUNCH of them and get a general idea of what a coin is supposed to look like for a grade. 99% of counterfeits have a style that is different than a genuine coin in the same grade.
ebay is a good resource for this (at least for capped bust
Half Dimes) as 99.9999% of the coins are genuine. Also look at fakes (if you want me to post pictures of a couple fakes, I can) and try to discern how and why they are different.
If you still have doubts, match it to a known die variety. Sometimes the weird thing that catches your eye is a diagnostic for a variety.
http://www.everythinghalfdimes.com