Yeah there are minuscule differences in releases with a couple of the rainbow ponies. Moonstone and parasol were re-released with the second set of rainbow ponies and they tend to have slight differences. Also rainbow ponies from across the globe have slight differences due to batch differences. They were also released as mail orders too. So different batch differences and releases tend to make these notable variations for the rainbow ponies hard to keep track of. It doesn't really effect the value, unless someone is specifically looking for said variation and even then, it might only effect the value by a dollar or so!
Hope this helps!