We form a number from three consecutive tickets. If we write these digits in reverse order and subtract the original number from the resulting number, we always get a difference of 198.
If the digits are $a-1, a, a+1$, then one number is $100(a-1)+10 a+(a+1)$, and the other number is $100(a+1)+10 a+(a-1)$; the difference between these two numbers is: $100(a+1)+10 a+(a-1)-100(a-1)-10 a-(a+1)=200-2=198$.