The last digit of a ticket number is a
check digit. To quote something I wrote for a different audience:
A check digit is a digit that is calculated from the other digits of a number. When the entire number, including the check digit, is entered, a computer repeats the calculation. If it comes up with the same check digit, processing can proceed. If it doesn’t, it informs the user of a data entry error.
One might think random check digits will be correct one time in ten. However, human errors aren’t random. Most errors involve pressing a key next to the correct one or transposing adjacent digits. Check digits can protect against 100% of those. Since other errors are rare, check digits are effective overall.
Credit card numbers also always include check digits. One of the criticisms of U.S. Social Security numbers is that they do not; if you make a mistake in entering yours, you will probably have entered a valid number that belongs to someone else. (When SSNs were introduced in the 1930s, nobody worried about that sort of thing.) Most more recent national identifiers include one.