Arguably the most important part of a Cutie Mark is the Glyph, here meant to refer to the image depicted. It is from this that we gain the most significant indication of a pony's talent. That said, there is a fair amount of interpretation involved in reading Cutie marks. For example, Cheerilee's Cutie Mark, a Triune of Smiling Daisies is meant to represent her skill and passion for teaching. She described the mark in the episode "Call of the Cutie"
What this tells us is that apart from the pure symbolism inherent in the Cutie Mark, a pony's personal understanding of it can play a significant role as well. This presents us with a bit of a Dilema. Using the system that I have devised would not give us the best understanding of a mark like Cheerilee's. The question then is this; How do we handle the subjective meanings of Cutie Marks?
One possibility would be to simply disregard this aspect of Cutie Mark Interpretation as it makes the entire exercise a foregone conclusion if you already have an idea of what a Cutie Mark means. In it's capacity as a tool for character creation, this would be a perfectly tenable solution, but in it's secondary purpose of reading meaning from existing marks, this falls short. I recognize that it would be impossible to systematically derive the subjective meaning from a mark so I'm still left with the question of how to do it.
As always, your input is welcome and encouraged.