法兰克福到比利时ICE列车预订座位

5月9日从法兰克福到比利时，我买了欧洲21国通票，请问如果5月8日或9日当天到火车站预订座位是否会有订不到座位的情况？




另外，关于是否一定要ICE预订座位的问题，在http://www.eurail.com/europe-by-train/high-speed-trains/ice 查到了一下信息：
“Reservations on regular ICE high-speed trains are optional. Reservations are mandatory on the ICE from Frankfurt to Paris and on the fast ICE sprinters. Between June 14 and August 31, reservations are also mandatory on the ICE between Germany and Denmark.
Please keep in mind that the ICE on the route Frankfurt - Paris has limited seats for Eurail pass holders. Make sure to reserve your seat well in time. You can make reservations up to 3 months in advance.”


这是不是意味着法兰克福到比利时不是必须预订座位了？