This app goes off of idgb’s franchise and series listing, but only the first tag that shows up will be on GameTrack. For example, New Super Mario Bros 2 isn’t showing up in the New Super Mario Bros series category, because it also shows up in the Super Mario and Mario series, and was added to one of those first on igdb. This game should show up in all of them.
Also adress spin off games showing up in the “in this series” label, because idgb requires the first entry in a spinoff to be labeled as such but not the subsequent entries. The spinoff should only show up with the “in this series” label if on igdb it’s marked in both the series and spinoff categories at the same time, which does happen.