Yes, the PMB Matto and Forza cards are by different artists. That has been recognized for a long time. Forza is one of 6 cards (along with Temperance, Star, Moon, Sun, and World) by a different artist than the others, of a style popular later than that of the first artist. Whether they were made as replacement cards, as additional cards, or are from a different deck is not known.
In my view the "first artist" cards are from 1452-1456, done by the Bembo workshop in Cremona. Actually, two different hands have been detected in these cards, that of Bonifacio in most of the triumph and court cards and that of his brother Ambrogio for the number cards (so I say 1456 because Bonifacio left Cremona to do work elsewhre for the Sforzas in 1455, which might have left his brother to finish up). It is my suspicion that these cards are not the first deck of its type, because of the presence of the Venetian lion in the King of Swords card. Francesco Sforza had not worked for Venice since 1448 (or thereabouts). They may have been for Sigimondo Malatesta, known to have requested a deck "with all the ducal insignia" in 1452. There is also Bartolomeo Colleoni, who was elevated to the position of captain-general of Venice's forces in 1455. That the cards were in the possession of the Colleoni family starting in the 18th century (I think it was then) may be owing to the family's wanting to have their famous ancestor's (or namesake's) deck. Accepting such a deck, with its ducal insignia, would be a tacit acknowledgement of Francesco's right to be called duke.
For the six triumphs in a later style, the art historians all assign them to Antonio Cicognara, attested from 1480 to 1515 (see Sandrina Bandera in "Quelle carte de triumphi che se fanno a Cremona", I tarocchi dei Bembo
, 2013, p. 50). However tarot researchers tend to make them earlier. Since the motif at the bottom of the cliff face continues from the original cards to the new ones, the artist would have had access to the previous cards or sketches of them--unless such cliff faces were a standard feature of decks of the "Visconti-Sforza" type. Another reason for assigning them to the 1480s or 1490s (besides the association with Cicognara) is that the Forza card seems modeled on the picture of the 26th degree of Libra as seen in Johann Engel's Astrolabium Planum
, first published 1488 Augsburg and again in 1494 Venice. Ross Caldwell noticed the similarity but thought that the Schifanoia imagery of the decans was based on the same imagery, originally that of the 13th century scholar Pietro d'Abano. If so the card could be of the time of the Schifanoia, c. 1470. But in fact the imagery of the Schifanoia is based on a different book, the Picatrix, as I pointed out in a recent THF post (viewtopic.php?f=11&t=1193&p=19582#p19582
). So unless the PMB 2nd artist had access to Engel's drawings considerably before he published them (Engel was in Germany), there is no reason to think that the PMB Forza card is earlier than 1488, or even around 1494, the date of the Venice edition of the book.
On the issue of decks and artists I question whether it is useful to show the "repros", as they are totally redrawn images that obscure the different styles. In one version I have seen (that in Lo Scareabo's book The Visconti Tarots
) the cliff face is even removed from the bottom of the Matto card! (In the version you have, it is instead exaggerated.) Also, the Popess's robe, in the original, seems different, at least in paint, from the rest of her, suggesting that at some point it was retouched ("restored"); the same is true of the Old Man. The paint looks similar to that of the 2nd artist cards. While for purposes of comparing standing vs. sitting, your "repros" are OK, for other issues you need to use genuine photographic reproductions. If you google "merge images" you will find an online tool that will merge the individual images to suit your purposes.
Added later in the day:
If the original PMB was for one of Francesco's fellow condottiere, in Venice, I am not sure what that does to the "2nd artist" cards. Perhaps they were Duke Ludovico's gesture of thanks for their support in getting acknowledged at last by the emperor. If so, then perhaps they are indeed "added cards" as opposed to replacements, as Huck has maintained for a long time. Or they are from another deck; it seems to me impossible to say.