Poetic licence by the setter perhaps? And people know C is the numeral for 100, that the Roman system puts the number to be subtracted in front of the one it is subtracted from, and that 100 less 1 is 99. So not unreasonable clueing? As you would struggle to find a word that had XCIX in order in…… let alone one that left you with another word when those letters were removed.
11d is a gem of a hidden when you think he sang from the bottom of my heart! I think quite a few of his hits were R&B.