Hi Lord Adonia,
It is true that I branch out on some of the cards; the Rosetta Tarot is not intended to be a slavish clone of the Thoth but rather a Thoth-inspired deck. I love the Thoth deck, but the design for the 9 of Disks in it I found rather uninspiring.
Maybe this will help you see how it does relate to the Thoth:
The "sliding pegs" you refer to are the emerald green beads of an abacus, a device used for counting and calculating sums, usually by merchants.
Crowley says of Gain, the Nine of Disks, that "it reckons up its winnings; it does not worry its head about whether anything is won when all is won. This card is ruled by Venus. It purrs with satisfaction at having harvested what it has sowed; it rubs its hands and sits at ease." (Book of Thoth, pg 187)
It is Venus in Virgo - and astrologically, Venus rules money while Virgo rules accounting.
As I say in the Book of Seshet, Venus loves luxury and Virgo loves counting.
The four scales of Venus are Emerald Green, Sky Blue, spring Green, Bright Rose or cerise, rayed pale green. The four color scales of Virgo are yellowish green, slate grey, green grey and Plum. The Princess Scale for Yesod is Citrine, flecked azure.
As I have incorporated most of those colors in the design, the color scales have been followed. I think that due to Aleister's commentary in BOT, the astrological attributions, and also the Golden Dawn color scales this card thus both follows the Thoth deck as the basis and preserves the occult meaning, but of course I would
