The inspiration for the imagery in many of the trump cards in the Rare Triumphs comes from early and regional Italian tarot cards and related artwork. Very early examples of Italian tarots include the various hand-painted and gilded Visconti type tarots. Regional patterns include Bolognese, Florentine (Minchiate), and Sicilian patterns. Some of these regional designs are still produced and used for tarot games - the designs have changed relatively little over the years since they first appeared. So some of the trump cards in the Rare Triumphs use very classical imagery from these traditions.
Looking at these old tarot designs, it is clear that for most of the cards there is more than one typical image that can represent a particular subject. For example, strength may be represented by a lady with a lion (specifically a lady astride a lion's back with her hands around the lion's jaws) ... or it may be represented by a lady with a falling pillar. Or a variety of things may be happening underneath the sun, moon, and stars. Many of the cards have these kinds of variation.
Another source of the imagery in the Rare Triumphs is the so-called "Mantegna tarot". Some of the lower-numbered trump cards in the Rare Triumphs form a sequence based on the states of man on earth, similarly to the states of man images in the so-called "Mantegna tarot". A lot of the imagery in the so-called "Mantegna tarot" is shared with tarot cards, though these images are not actually tarot cards themselves.
Mitelli's tarot has an interesting approach. The art style is rather more sophisticated in its appearance than the simpler, more naive woodcuts typical of many old tarots. But the subjects themselves are rather stripped down or alternative representations. Some of them are drawn in an unusual or maybe even unique way. For example, the lightning card just has a man being struck by lightning; instead of a hanged man, we see a rather explicit act of betrayal illustrated on the card. In the end I didn't follow Mitelli on either of these two cards, but you may see reflections of the Mitelli tarot elsewhere in the Rare Triumphs, as well as perhaps in my overall way of thinking.
The Catelin Geofroy and Anonymous Parisian tarots are unusual. They are both French woodcut tarots, but their illustrations are rather eclectic. You may see some aspects of the imagery in the Rare Triumphs that might be inspired by these two. It is also interesting to consider the pip suits of these tarots. The Catelin Geofroy is very unusual in that it has suits of birds (notably it has this in common with a probable ancestor of tarot described by Marziano da Tortona; bird suits were also found in German playing cards, and I remember looking through these bird-suited cards at the time when I was making my first set of playing cards, in the style of German hunting decks, with two bird suits). The anonymous Parisian tarot has the usual tarot suits, and yet things are not quite as usual as they might seem ... the suits are not drawn in the Italian style with straight batons and curved swords (as seen in almost every old-style tarot deck, including Marseilles cards), but in a way resembling Spanish playing cards. So probably the most significant thing my cards have in common with these two classic Parisian sets of cards is that they have a less typical set of suits!
Finally I will mention the Vieville tarot and the related regional tarot tradition called Flemish or Brussels-Rouen tarot. One of the cards in the Rare Triumphs is clearly drawn in a characteristic way based on the imagery from this family of historical tarots.
This should give a bit more insight into my influences in drawing the trump cards for the Rare Triumphs. I have been quite general in what I have written here, but it might give you at least some insight into where I am coming from, and even into what sort of historical cards are out there if you want to look into it further.
You can order the Rare Triumphs tarot cards here.