Hi Bryn,
I probably wouldn't have picked the differences a few years ago, either. It's all a matter of training the eye. Just recently, the whole Australian carnival collecting scene has had to become a lot more careful about noting very subtle differences in shape, angle, curves, relative sizes and distances, because they have had to deal with fakes - and because they'd never had the problem before, very experienced people have been fooled.
It's all good experience.