IC vs XCIX

Why IC is not a valid form for 99 and XCIX is correct.

IC is not the standard modern canonical form for 99.

XCIX

99 in Roman numerals is XCIX.

Check in tool 99 encyclopedia page

What is wrong

Only IV, IX, XL, XC, CD, and CM are valid subtractive pairs.

Canonical form

XCIX is produced by this site’s conversion engine for 99.

Related mistakes

IIII vs IV VIIII vs IX IL vs XLIX Roman Numeral Subtractive Pairs