In his beer-themed Guardian crossword yesterday, Qaos was forced to alter "mild" at the last minute to "bird" (because "mild" had appeared in the previous day's puzzle).
He kindly explained on fifteensquared, and said that the intended clue was based on "1049 + 500" (MIL + D).
By the convention that, in a subtractive formation, the value of the first letter must be at least 1/10 the value of the second letter, "IL" for 49 is just as wrong as the commoner (in crosswords) "IC = 99".
However, by that rule, LD is valid, so "1001 + 450" would have been OK. The problem is that I don't recall ever having seen "LD" used for 450 - has anyone else come across it?