Roozaimu43
Important: As Danhiel already indicated, you don’t need the half fare card for BUYING discounted tickets, but for TRAVELING with discounted tickets. Therefore the dates on the half fare card must match your effective travel dates.
BTW there’s no reason buying regular train tickets now, as their availability is unlimited so they never sell out. You could also buy them 10 minutes before departure for the same price (or during breakfast at the hotel, after checking the current weather conditions at your destination on webcams).
Unless you’re chasing some saver tickets, which do “sell out” regarding a particular price point, but beware, the refund conditions for those are VERY limited!