Huck
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... you've to understand a few things about Trionfi decks, the appearance of the name "Tarot" and also about the development of astrology and astronomy studies during 15th century, if you wish to follow your hypothesis. This might become quite time consuming.First to the Trionfi decks: The use of this name for a specific sort of playing cards started for the perspective of current research in September 1440 ... or earlier, but this isn't proven.
For the name "Tarot": The use of similar names (Tarochi or Tarau) appeared first in 1505 in Ferrara and in the same year in Avignon. "Tarocchi" or "Tarot" forms followed some time later.
Tarot Research around 1980 was based on the hypothesis, that "Trionfi decks" were "Tarot decks", in the sense, that they had the same number of cards (78 in a 4x14+22 - structure) and similar motifs and a similar row of these motifs (though with differences), at least since 1450.
This hypothesis found stronger opposition since 2003.
According this alternative opinion there was a longer period of deck experiments with other numbers of trumps. Decks with 5x14-structure are discussed, decks with 16 and 20 trumps are suspected. As earliest surviving deck with 4x14+22 - structure the Boiardo Tarocchi poem of Matteo Maria Boiardo is accepted ... a plausible date for this production is as late as 1487. The content of this deck (motifs and suits) is quite different from the common Tarot).
For the moment there are researchers, which follow the old hypothesis, and there are researchers, which follow the alternative.
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Astronomy in 15th century (with special interest on Ferrara)
The new German emperor Frederick III (started 1439 and reigned till 1493, a long time) had specific interest in astrology and astronomy. Also he had splendid relations to the Enea Piccolomini, later pope Pius II, but earlier secretary of Frederick.
This led to the condition, that the university of Vienna had rather good astronomers, especially Georg von Peurbach, and later Peurbach's pupil Regiomontanus.
Peurbach gave astronomical lectures in Ferrara in c. 1448-1449. There was a specific young astronomer between his pupils, Pellegrino Prisciani, who later became of influence in Ferrara.
Around the same time a Ptolemy (a famous old astronomer) work became of great interest
in Rome, which was then ruled by Pope Nicholas, who sponsored the translation from Greek to Latin. This was a long work and it took years and it got a lot of critique.
When Piccolomini became pope in 1458, he demanded, that Peurbach as the true specialist should come to Italy. But Peurbach had just died, and so Regiomontanus came instead. This was 1461.
Meanwhile in interest in astronomy and the cosmological conditions (world maps, world globes etc.) was increased ... since 1454 Italy had peace and needed not so much money for its wars. Regiomontanus found great interest in Italy, especially in Ferrara (which was ruled by Borso d'Este then). Borso started to realize the Palazzo Schiffanoia as an expression of the increased astronomical interest since 1469, Regiomontanus had followed meanwhile a call of the king of Hungary, Matthias Corvinus.
Pellegrino Prisciani, meanwhile of influence, designed the program according the poem of an antique astrologer. This activity caused other astronomical projects in Ferrara, Ferrara had a book printing house with the focus on astronomical themes. Parallel in Nuremberg Regiomontanus, meanwhile back from Hungary, made an own publishing house for astronomical texts. This happened around 1472/74.
For the Hyginus text (realized by a German engraver) we have, that it is assumed, that it had a Ferrarese (lost) forerunner, made in the mid 1470s. The production has some internal logic, as this projects fits well with the Manilius text.
1470 is the year, when Italian book printing jumped to high numbers. We have other astronomical projects in Rome (1473-78), again with the participation of Regiomontanus (who died in Rome), astronomy had been of great interest then.
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Ferrara is proven to have taken a greater influence on the Trionfi card development. Especially it's remarkable, that they made creative side steps, away from common Tarot style to alternative decks like the Boiardo Tarocchi and the Sola Busca Tarocchi.
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For the two different interpretations of the Trionfi card development: The idea, that Tarot was ready in a fixed manner c. 1450, doesn't leave the chance of an influence of star pictures in the manner of the Hyginus texts.
The assumption of a longer creative development with a diversity of side steps allows much more freedom.
