One of the things people get confused about in terms of their elemental type or dosha is the difference between their birth dosha and their current condition.
At birth you come into this world with your own particular ratio of the five elements that make up everything in the universe, including you. This birth constitution is called your Prakriti in Ayurveda.
Although all three doshas (and their corresponding qualities) are present in all things, there is usually one or two doshas that are more prevalent in each of us at birth. This does not change throughout our life time. Your Prakriti is your Prakriti. You are you.
However, since we all have at least some of all three doshas, we can become unbalanced in any one of them. For example, even if you are a Vata type by birth, you can still experience a “Pitta overload”. All that means is you’ve added too much of the qualities that are present in Pitta (sharp, hot, liquid etc) to your constitution through the lifestyle choices you make.
Having said that, you have more of a tendency for overload in the qualities you already possess more of. Vata types for example are light, subtle, cool and mobile by nature. These qualities are more likely to become overloaded simply because by nature, Vata already has more of these qualities to begin with.
Generally, Ayurvedic practitioners are working primarily with your current imbalance (Vikruti) but also factor in your general health history, your birth constitution (Prakriti) and your current lifestyle to come up with the best treatment plan for you.