The wiki voice on Ophichus clearly states that Schmidt and succesively Berg had the idea to include Ophiuchus into the zodiac. According to the 1930IAU constellation boundaries, the sun would cross the Ophiucus field.
That's the source of Walter Berg's hypothesis and model.
Now, I'm not able to falsify or verify that.
Ophiuchus (⛎) (/ɒfiˈjuːkəs/) has sometimes been used in sidereal astrology as a thirteenth sign in addition to the twelve signs of the tropical Zodiac, because the eponymous constellation Ophiuchus (Greek: Ὀφιοῦχος "Serpent-bearer") as defined by the 1930 IAU constellation boundaries is situated behind the sun between November 29 to December 17.[1]
The idea appears to have originated in 1970 with Stephen Schmidt's suggestion of a 14-sign zodiac (also including Cetus as a sign). A 13-sign zodiac has been suggested by Walter Berg and by Mark Yazaki in 1995, a suggestion that achieved some popularity in Japan, where Ophiuchus is known as Hebitsukai-Za (へびつかい座?, "The Serpent Bearer").
In sidereal and tropical astrology (including sun sign astrology) a 12-sign zodiac is used based on dividing the ecliptic into 12 equal parts rather than the IAU constellation boundaries. That is, astrological signs do not correspond to the actual constellations which are their namesakes, particularly not in the case of the tropical system where the divisions are fixed relative to the equinox, moving relative to the constellations.
...Based on the 1930 IAU constellation boundaries, suggestions that "there are really 13 astrological signs" because "the Sun is in the sign of Ophiuchus" between November 29 and December 17 have been published since at least the 1970s.[5]
In 1970, Stephen Schmidt in his Astrology 14 advocated a 14-sign zodiac, introducing Ophiuchus (December 6 to December 31) and Cetus (May 12 to June 6) as new signs.[6] Within 20th-century sidereal astrology, the idea was taken up by Walter Berg in his The 13 Signs of the Zodiac (1995). Berg's The 13 Signs of the Zodiac was published in Japan in 1996 and became a bestseller, and Berg's system has since been comparatively widespread in Japanese pop culture, appearing for example in the Final Fantasy video game series and the manga and anime series Fairy Tail.
In January 2011, a statement by Parke Kunkle of the Minnesota Planetarium Society repeating the idea of "the 13th zodiac sign Ophiuchus" made some headlines in the popular press.[7] However, Kunkle is an astronomer, not an astrologer.[8]
