1:02:03 04/05/06

[na_th_an]

for 1988 can you shorten it to something like XIIMM ? twelve before two thousand?

You can't. The rule states that the substraction can only be done with the immediate anterior figure which is a power of 10, i.e. you can only substract I from X, X from L or C, C from D or M, and so on. And you can just substract 1 power of 10, i.e. you can just make IX, XL, XC, CD and CM.

That's the only way to have a perfect set of rules, i.e., you can only represent a number with just one concrete string. If the substraction rules were more flexible, you could write 8 as VIII, as IIX, and whatever you could fancy, which is not very practical.