You must write in the date of your ticket prior to ticket inspection by the conductors. Only once have I seen a conductor make a big deal about forgetting to do so. usually they will write it in for you if you forget. Please be aware that there are a limited amount of seats on any train that are sold to eurail pass holders. There are usually seats available for full fare tickets. Some train lines, such as the night trains from Paris to cities in Italy or from Rome to Paris, may be sold out for pass holders 2 to 3 months in advance. On a recent trip through France and Italy I had to pay full fare on two occasions because the tickets alotted for pass holders were sold out. I had a 6 day pass but was able to use it only 4 times. While the savings with the pass are good you cannot always count on getting the train you want. This is not good if you are on a tight or fixed schedule.