Is it a stupid idea to have another word for twelve?
Again that is limiting the problem to our way of thinking. CXII = C + X + II so if you wish to multiply it by XIV you multiply (C+X+II).(X+IV) = C.X + C.IV + X.X + X.IV + II.X + II.IV = M + CD + C + XL + XX + IIX = MDLXIIX. You can make your life even easier thinking of IV as V - I.