Yeah the reason for the naming is that the original games were Trails in the Sky FC (First Chapter) and SC (Second Chapter) because it was supposed to be one game. And the scope of the story got so huge that it would never have been reasonable to release it as just a single game. FC was a 40-60 hour game while SC was 60-80 hours.

The 20 hour gap on each is really how much a player dug in because nearly every single NPC has their own story going on in the sidelines and some people (myself included) actually end up following them all at every story transition. They reoccur throughout this game and later games too, so the attention to detail to keep an these things happening is fairly incredible.

To further answer your original question though, FC really does need SC to get a satisfying end, but FC is a beloved entry anyhow from all the world building it provides.

The series is currently 12 games and will be 13 soon. That’s 4 major story arcs that all connect, get referenced, have some reappearing characters and talk of those past events, etc. In comparison to more well known JRPG series, it’s not like Final Fantasy or Dragon Quest because this is not an anthology series.