I was asked about Ophiucus today. This is a constellation that the Sun passes through from November 29th to December 17th. It is considered by a very few astrologers (mostly those who use the Sidereal House system) to be the 13th sign of the Zodiac. Most astrologer refute this claim, stating that the traditional definition of the Zodiac is a division of the path of the Sun across the sky (the Ecliptic) into 12 equal signs. Also, there is a difference between Zodiac signs and the constellations. The signs represent an evolutionary journey. They are not based on the actual, physical position of the constellations in the sky today (Sidereal astrology, however, is based on the constellations).
Ophiuchus is identified with Aesculapius, a demi-god. Aesculapius was the son of Apollo and the princess Coronis. He is associated with healing and destruction, as symbolized by the staff with a serpent wound around it (the serpent can kill with its bite but also sheds its skin as a symbol of regeneration).
So, what to do? Should the horoscope books be revised? What if your birthday falls between these dates? Honestly, nothing has changed so I wouldn't get hung up on it. The existing astrological system still works (as it has for centuries). I can't say at this point if it's valid or not because I've never used this sign. But I don't think it's a bad thing to question an established system, even if it turns out to be bunk. Pluto (transformation) is moving through Capricorn (establishment) after all.