A student just asked a great question:
"If an astrologer sees something about the past, but that didn't materialize, does it give a clue about the kind of karma that the native built up? Meaning, can retrodiction [a prediction about the past] be used to live more intelligently in the future?"
Here is my answer: If the retrodiction failed, then the astrologer failed. Sorry if that seems harsh, but that is my first answer. Building on it, that simply means that the astrologer is still learning, and very few astrologers are not still learning. What it can do is teach you something new, or at least stimulate you to learn more, some new technique, some new meaning.
So, at the very least, it can cause the astrologer to live more intelligently into the future. The client is just fine, always has been and always will be (and so is the astrologer).
Now, I feel like latently embedded in that answer is another question about free will. That is, some may say that the person is "just" exercising free will, and that is not in the chart. The concept of free will is held in such high esteem in American culture, and so, if your astrology can not line up with a past event, it is not helpful or even honorable, the thinking might go. I would like to address that thinking.
Remember that astrology is fundamentally about maya, and in maya is great cause and effect, such a dense web of it in fact that almost everything is fixed in potential in the chart. This is the field of experience, and the astrologer excels here.
There is in fact only one thing not in the chart: Purusha consciousness, "one-pointed awareness", also the only thing which gives us real freedom and hence real free will. It is true; that is beyond the chart, always has been and always will be. (In one-pointedness is no movement, no change, nothing to move into or change into, so the melodramas of the stars are of no use.) Hence, It is beyond the laws of karma and is the pure essence of everything, including Itself. This is the seed of awareness, and personal consciousness excels here. This is reality.
However, what does Purusha consciousness want to fulfill? Prakriti (Mahamaya), just as Shiva wants to fulfill Parvati, leading us in a delightful mobius strip back to the astrology chart.
This is why Dr. Lad draws an infinity symbol between Purusha and Prakriti at the top of the Sankhya tree.
To know this diagram is to know astrology, to know Ayurveda, to know both the manifest world and where it came, to know the child of Purusha and Prakriti. Ganesha.
Note: above Purusha and Prakriti is the unary oneness of Atman. Atman is not shown in this particular version, but in school, when presenting this topic, Dr. Lad does certainly draw It.
Aum Shreem Hreem Kleem Glaum Gam Ganapataye Swaha!