I'm finally home after 7-weeks away. If you would like to pursue this topic further, I can delve into my archives of academic articles for citations.
At page 172 Neugebauer states ''This shows that the longitudes in Vettius Valens are sidereal longitudes whereas the later authors operate with tropical longitudes obviously following the norm adopted by Ptolemy and Theon.''
Not all later according to recent (we should recognize that Neugebauer did not have access to all Hellenistic and Egyptian sources) academic sources I have cited here who report ''abundant evidence'' of sidereal conversion -
http://skyscript.co.uk/forums/viewtopic.php?t=9957&start=15
I have found that the Palchus horoscopes with degrees to have great amount of accuracy with Aldebaran 15, usually the exact for the Sun, Moon and a few stars. During the making of this I may post his charts too.
Yes, I believe it is worth discussing this with you. I have been interested in making a list of all Valens' charts sidereal by tropical anyways to show the difference for quite a while now. I will start in the order that Neugebauer listed them. Get a software, set your city to Alexandria and let's begin.
1. Sun - Scorpio
Moon - Cancer
Saturn - Aquarius
Jupiter - Sagittarius
Mars! - Scorpio
Venus - Libra
Mercury - Scorpio
Asc - Libra
Neugebauer computes it for 25 October 50 AD (he uses Julian) and notes that Mars is at 27 Libra. Mars is in Scorpio with Spica zodiacs (I will use this term as convention for later than a degree than Aldebaran), in Aldebaran it is at 29 Libra. No other date is possible with Mercury position, however you might say that Mars was hard to calculate and frequently wrong, that could certainly be the case, but if too many cases are like that on average, then it is likely to indicate a different zodiac, based on statistics. Spica zodiac - 1. Moving on.
2. Sun, Venus, Asc - Taurus
Moon - Aquarius
Saturn! - Cancer
Jupiter - Libra
Mars and Mercury - Gemini
Neugebauer computes this for sunrise 1 May 61 and notes later that Valens uses the Babylonian System A for rising times. In tropical, Saturn is in Gemini.
(Aldebaran - 1, Spica - 2)
3. Sun - Aquarius
Moon and Jupiter - Scorpio
Saturn - Cancer
Mars!!, Venus! and Mercury - Capricorn
Asc - Pisces
Computed for 22 January 62 about 10 a.m. Notes that Venus is in Sagittarius with tropical, but that Mars is a sign and a bit away from its position given in the text, and he gives the opinion that is a mistake in the text for Scorpio as such errors are unusual. That being said, the chart once again does not work with tropical longitudes. (Tropical - 0, Aldebaran - 2, Spica - 3)
4. Sun, Moon and Mercury - Gemini
Saturn - Leo
Jupiter - Pisces
Mars - Cancer
Venus - Aries
Asc - Capricorn
Neugi finds ''excellent agreement'' for 24 May 65 about 8 p.m. Works with all zodiacs. (Tropical - 1, Aldebaran - 3, Spica - 4 out of four)
5. Sun and Mercury - Scorpio
Moon - Aries
Saturn - Virgo
Jupiter - Pisces
Mars - Leo
Venus - Sagittarius
Neugebauer finds this horoscope problematic and has 31 October 65 about 8 a.m. as a tentative date. Venus and Mars are in Libra...
I checked 27 October 125 which I find more plausible, three stars are in wrong signs, but they are slightly nearer their hypothetical positions and I can imagine Mercury and Jupiter being slightly off by a few degrees and Mars with a sign. I wonder if I should even count this, but I will count 1 for all. (Tropical - 2, Aldebaran - 4, Spica - 5 out of five) I will continue in a subsequent post, preferably in another thread, as I do not have anything more to discuss with the op.