Didn´t know that the months are divided in two parts.
But I guess there are different ways of classification around.
Like if you go to some jeweller´s site http://www.bernardine.com/birthstone/pisces.htm
they come up with a lot of stones, probably so they can sell more stuff. 😉
The Jewelers are more interested in selling their stuff, the traditional astrologers do the same.
In Crystals it is best to go with your intuition rather than others suggestions. What you get energetically drawn to is best meant for you then it can be the cheapest one no problem. They come to you at the right time for your right need in life.
There are 12 months simple advised crystals also, but this is going a little deeper to be more specific :-)
Thank you for stopping by @likedeeler :-)