As far as I understand this “left out” star literally is left out. It is supposed to be the star Vega, and the surrounding stars – which is in the constellation of Lyra, which is way outside of the zodiac area. In fact, Vega becomes the Dhruva, the polestar, every 26,000 years. In other words it is way up north and outside the ecliptic belt of the zodiac. This a valid reason to leave it out of the calculations of planetary positions. If you trace it’s position downward into the ecliptic it slides in between Uttarāṣāḍhā and Śravaṇa. Some have said that it is a theoretical area that pertains to time rather than space and is therefore of importance to determining auspicious times of day, and not to calculating or describing planetary positions.
For the present, at least, I feel it is safe to omit Abhijit from my system of natal astrology. But I will keep my ears and mind open towards it.