My guess would be that people type in all sorts of numbers copied from the ticket where the form asks for a ticket number, and the people handling the claim just type in whatever appears on the scan. If I'm right, I expect they'll stop asking for ticket numbers altogether at some point. Where I think it would be useful for ticket numbers to be made clearer is with advance tickets which have separate reservation coupons. The ticket number is in large print at the top of the coupon, but only in small print at the bottom of the ticket, with a big blank space at the top. And it probably would be an idea if it didn't refer to "the booked services below" when the reservations aren't on the ticket.