Why does the astrologer say that each person is unique when there are only 12 zodiac signs?

In Vedic astrology, the 360 degrees of the Earth are divided among twelve zodiac signs, with each zodiac sign having 30 degrees, and thus twelve zodiac signs namely Aries (Mesh), Taurus (Vrishabh), Gemini (Mithun), Cancer (Kark), Leo (Simha), Virgo (Kanya), Libra (Tula), Scorpio (Vrishchik), Sagittarius (Dhanu), Capricorn (Makar), Aquarius (Kumbha), and Pisces (Meen) are mentioned. Similarly, twenty-seven constellations (Nakshatras) are divided such that each zodiac sign, meaning 30 degrees, contains two and a quarter Nakshatras.

The span of one Nakshatra is 13 degrees and 20 minutes (Kalas), and each Nakshatra has four quarters (Charans) of 3 degrees and 20 minutes each. The lord of each sign, Nakshatra lord, and Charan lord are fixed, and there is never any change in them.

In astrology, since Rahu and Ketu are shadow planets (Chhaya Grahas), they have not been given the lordship of any zodiac sign. The significations of constellations and houses never change, they are fixed; whereas the planets present in the houses, the ascendant in the chart, the degrees of the ascendant, the planets-constellations in the ascendant, the planets casting an aspect on a house, the planets forming a conjunction in a house, and because of each 3 degrees and 20 minutes having different quarter (Charan) lords, their influence, the element of the ascendant, the position of the ascendant lord in the chart, the auspicious-inauspicious combinations formed by the nine planets from different positions in the chart, the planetary periods (Mahadasha-Antardasha periods), and the transit of planets keep changing according to the cycle of time, and the prediction of outcomes also changes accordingly.

The ascendant (Lagna) in astrology means the zodiac sign rising on the eastern horizon. The 30-degree duration of that zodiac sign means the ascendant in astrology / the birth chart, and this ascendant lasts for approximately two hours. That is, in 23 hours and 56 minutes, this ascendant point moves forward every four minutes because it takes four minutes to progress each degree.

Astrology is a deep and boundless science; even further subtle predictions are stated through the Shodashvarga. Shodashvarga means the 16 different types of charts generated from different divisional charts of the main birth chart (Lagna Kundali), which are: Lagna (D-1), Hora (D-2), Drekkana (D-3), Chaturthamsa (D-4), Saptamsa (D-7), Navamsa (D-9), Dasamsa (D-10), Dwadasamsa (D-12), Shodasamsa (D-16), Vimsamsa (D-20), Saptavimsamsa (D-27), Chaturvimsamsa (D-24), Trimsamsa (D-30), Khavedamsa (D-40), Akshavedamsa (D-45), and Shastiamsa (D-60).

Such a deep study, and that too being different for each individual — the primary reason for this is that in astrology, except for the houses and constellations, everything else is moving (mobile) and it keeps changing constantly with time; therefore, it is not true that the predictions will remain the same just because of the twelve zodiac signs. Just as every person's fingerprints are unique, similarly, the astrological prediction of outcomes is different for every individual.