Three boats of three different sizes work these routes, so the number of seats changes from sailing to sailing. The forty eight seat boat does the busy commuter runs, the forty two seat boat covers most of the rest, and a thirty six seat boat takes the quiet midweek ones.
Every one of those numbers is in the system, which is why a sailing here can show as full. The counter is looking at the same list you are.
When the timetable changes, and it does with the season, this page changes the same morning. There is no printed sheet somewhere contradicting it.