Note on the side: many USAers tend to think they are and have to use that specific train-in actual fact there are most often dozens of alternatives-other times, other outings, perhaps with a change more. IN France only these superfast TGV trains MUST be reserved-but on domestic routes hese often run every hour or so. So if your wanted 9.55 is full (highly unlikely though) take the 8.55 or 10.55!

You can also check the availability of pass reservations in France on the Belgian railways website.