Now this is an interesting question, as the association of metals with certain days of the week is tied to the celestial bodies within our own crystal sphere, unknown to the people of Realmspace. The celestial objects they would potentially know would be, using the same criteria we did, the Sun, Selune, the Tears of Selune, Anadia, Coliar, Karpri, Chandos, Glyth, Garden, and H'Catha. That does add up to ten, assuming one counts the Tears of Selune as their own thing. However! In addition to the sun and moon, only Anadia, Coliar, Karpri, and Chandos are visible to the naked eye from Toril. So would a ten-metal system become a thing among local alchemists?