1808A - Lucky Numbers

In this question, If the ans of l = 1 to r = 9 is 9 (luckiest number)
Then why not the answer of l = 1 to r = 10 is 9! (luckiest number) Instead it is given as 10.

Condition for luckiest no. is that diff of highest digit of a no. with it's lowest digit.
eg: num = 992 so luckiness = 9 — 2 = 7