I don't think it is misleading, that is your personal belief regarding astrology and the higher self. Also, even if one believes that our astrology was different in past lives, the deck is about our astrology in this life, and how our soul experiences our current incarnation, in terms of our present astrological make-up. Of course if you could discover the astrology of your past life, you could apply that to the system in the book. In my view the popularised view of reincarnation is very much from Eastern theology and not necessarily the belief of the ancient Celts.
There seems little evidence of a doctrine of universal reincarnation among the Celts. It is clear that Spirits are often born into flesh for various reasons. For some, the Way of return is their fate. Those chosen by the Powers for some destiny, or who choose rebirth themselves, or are placed under a geas by a magician, may return to the mortal world to work out their path. For me, the Celts believed in the transmutation of souls in a more shamanistic approach.
There also seems little evidence that the Celts believed in a process of regular reincarnation leading to movement up any sort of spiritual ladder or stairway. Spirits came into flesh to aid their foik, to do the Gods' work, etc. Some ancient Celtic texts speak of procreation as the means of ongoing incarnations through their children. While holding a belief that we return to a paradise otherworld after death.