When the CST776CSG toilet comes with a seat, it becomes the MS776124CSG with the SS124 Soft Close seat.
C776CEGT40 bowl with connect hole for hiding the Washlet connections, thus needing the SS124 seat to cover the hole if the Washlet isn't used.
The standard CST776CEG has the C776CEG bowl without the Washlet Connect hole and can use any seat, including the SS114 Softclose.
They use the same tanks.