Though the ticket issue date is in full, the ticket coupon sectors and the internal queue commands to change them are in the format DDMMM, so 14SEP. Consequentially you cannot have any risk of 14Sep of 2024 being read over to 14Sep in 2025. So by limiting ticket validity you can get away with the sub-structure of the ticket not having the year explicitly mentioned. Remember the paper tickets and the details on the flight line (if you are old enough). But as already mentioned, BA is one of the airlines with the longest data ranges at 355 days, however with the possible exception of redemptions, one would be mad or unnecessarily rich to buy as soon as ticketing start.